chematic

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A cheminformatics library for Python, Rust, and the browser.

Cheminformatics that's fast by default, safe by design.
Pure Rust · Zero C/C++ · Python · WebAssembly · Website · Live Demo

* RDKit.js gzip-over-the-wire size was not independently measured; raw figures are compared on a like-for-like basis. RDKit.js is currently in a maintainer transition (see its repo for current status).

All numbers are reproducible — see benchmark details.
WASM sizes (raw, measured 2026-08-21 from a clean wasm-pack build --target web --release

• wasm-opt -O3, commit ef7dc25): chematic 2.94 MB (1.10 MB gzip) · RDKit.js 6.91 MB (@rdkit/rdkit@2025.3.4-1.0.0's RDKit_minimal.wasm, via unpkg.com) · Indigo (Ketcher build) 11.24 MB (indigo-ketcher@1.45.1's main .wasm, via jsDelivr) — chematic's raw WASM binary is currently about 2.3× smaller than RDKit.js's and about 3.8× smaller than Indigo's Ketcher-oriented build, on a raw-to-raw basis.

Feature maturity at a glance:

What you get

$ python -c "import chematic; print(chematic.from_smiles('CC(=O)Oc1ccccc1C(=O)O').describe())"
Molecular weight 180.2 Da, formula C9H8O4.
LogP 1.31 (mildly lipophilic), TPSA 63.6 Ų.
HBD 1, HBA 3, 3 rotatable bond(s), 1 aromatic ring(s).
Drug-likeness: no Lipinski rule-of-5 violations. likely orally bioavailable (passes Veber criteria).
QED 0.56 (0 = non-drug-like, 1 = ideal).
Structural alerts: Brenk alert.

One pip install. No RDKit, no conda, no C compiler. Works in Python, Rust, the browser, and AI agents.

# HTML report — self-contained, opens in any browser and renders in Jupyter
mols = [chematic.from_smiles(s) for s in smiles_list]
report = chematic.report(mols, names=compound_names)
report.save("report.html")   # or: display(report) in Jupyter

# Side-by-side comparison
cmp = chematic.compare(aspirin, ibuprofen, names=("Aspirin", "Ibuprofen"))
cmp.save("compare.html")

Common Use Cases

Full worked examples → Use cases

When to use chematic

Use chematic if:

• You want chemistry in the browser (WASM, 1.10 MB gzip, no server required)
• You need a pure Rust stack with no C++ toolchain dependencies
• You deploy to environments where installing RDKit is impractical or unsupported (Cloudflare Workers, Lambda, embedded — RDKit itself ships official pip install rdkit wheels, but those still assume a standard CPython environment)
• You build AI agents and want native MCP tool integration
• You process molecules in batch at high throughput (ECFP4: 2–3× faster than RDKit, Rayon-parallel)
• You want pip install chematic to just work — anywhere, no compiler needed

Use RDKit if:

• You need maximum ecosystem compatibility and 20+ years of production validation
• You need publication-quality 3D structures with ML-assisted torsion corrections (RDKit's ETKDGv3)
• You need bit-exact standard InChI without enabling the native-inchi feature
• You depend on community plugins written against the RDKit Python API

Choose your interface

• Rust
• Python
• WebAssembly / Node.js
• Materials and simulation formats — mmCIF, PQR, QCSchema, ORCA, Gaussian Cube, OpenDX, LAMMPS
• Migrating from RDKit — feature-by-feature Supported/Partial/Not-supported breakdown

Quick Start

Installation

# Python — no C/C++ compiler required
pip install chematic

# Rust
cargo add chematic --features "smiles,perception,chem,3d,fp"

# JavaScript/TypeScript
npm install @kent-tokyo/chematic

Python

import chematic

mol = chematic.from_smiles("CC(=O)Oc1ccccc1C(=O)O")  # aspirin

# In Jupyter, type `mol` in a cell — 2D structure renders automatically
mol

# Access 190+ descriptors as properties
print(mol.mw, mol.logp, mol.tpsa)           # 180.16  1.31  63.6
print(mol.lipinski_passes, mol.pains_passes) # True   True

# Substructure search
mol.has_substructure("[OH]")   # True
mol.find_matches("[CX3](=O)O") # → [[1, 2, 3], [7, 8, 9]]

# Natural-language summary (one paragraph)
print(mol.describe())

# Structured Markdown report — paste into LLM, Jupyter, or save as .md
print(mol.review())
# → # Molecular Review\n## Structure\n## Physical Properties\n## Drug-likeness\n## ADMET...

# Structural diff between two molecules
ibuprofen = chematic.from_smiles("CC(C)Cc1ccc(CC(C)C(=O)O)cc1")
d = mol.diff(ibuprofen)  # {"summary": "+C7, -O2. ΔLogP +2.75 ...", "delta_mw": 66.1, ...}

# Batch processing — parallel, numpy-ready
fps = chematic.bulk.ecfp4(["CCO", "c1ccccc1", "CC(=O)O"])  # (3, 2048) uint8

# One-liner DataFrame
df = chematic.descriptors_df(["CCO", "c1ccccc1", "CC(=O)O"])
df[["mw", "logp", "tpsa", "qed"]]

For Rust and JavaScript/TypeScript examples, see the documentation.

Migrating from RDKit

chematic.rdkit_compat provides a lightweight RDKit-compatible subset so existing scripts port with minimal changes:

from chematic import rdkit_compat as Chem
from chematic.rdkit_compat import Descriptors, rdMolDescriptors, DataStructs

mol = Chem.MolFromSmiles("CC(=O)Oc1ccccc1C(=O)O")
Descriptors.MolWt(mol)                       # 180.16
fp = rdMolDescriptors.GetMorganFingerprintAsBitVect(mol, 2, nBits=2048)
DataStructs.TanimotoSimilarity(fp, fp)       # 1.0

It is not a full RDKit clone, and unsupported options fail loudly. See the RDKit migration guide for the compatibility matrix, differential-validation results vs RDKit, and runnable examples.

Diagnostics

import chematic
chematic.doctor()
# chematic v0.25.0
# Python 3.12.x  |  darwin arm64
#
# Descriptor accuracy (benchmark 2026-07-17, v0.4.29 vs RDKit 2026.03.3 --
# descriptor calculation paths unchanged through v0.8.0, not re-measured since):
#   MW / HBA / HBD / ARC  100%   (4,999-mol ChEMBL subset)
#   TPSA                  100%   within ±0.1 Ų
#   LogP (Crippen)        100%*  (max Δ = 1.1×10⁻¹³)
#   Stereocenter count    99.96% (legacy) / 98.6% (new CIP FindPotentialStereo)
#   CIP R/S label         96.30% vs modern rdCIPLabeler (96.83% vs legacy)
# ...

For AI / LLM Developers

chematic ships a native MCP (Model Context Protocol) server — the first cheminformatics library with built-in AI agent integration.

// Claude Desktop (~/.config/claude/claude_desktop_config.json)
{
  "mcpServers": {
    "chematic": { "command": "chematic-mcp" }
  }
}

20 chemistry tools are callable from any MCP-compatible agent (full list in the chematic-mcp README):

Transport: stdio (JSON-RPC 2.0 over stdin/stdout) only. Runs as a local process; there is no hosted Remote MCP endpoint, no authentication, and no public service SLA — a remote-ready refactor is under consideration but not implemented.

Protocol: speaks both the legacy (2024-11-05-style initialize handshake) and the modern MCP 2026-07-28 stateless dialect (server/discover, per-request _meta, cacheable tools/list, structuredContent) on the same stdio connection — see the chematic-mcp README for the protocol details. Remote HTTP, OAuth, the Tasks extension, and MCP Apps remain unsupported.

Why Pure Rust?

Fast

Rust's zero-cost abstractions and ownership model eliminate overhead at the source. chematic's ECFP4 fingerprint batch pipeline runs at ~78 µs/mol on a diverse molecule corpus — 2–3× faster than RDKit's Python API on the same hardware, via Rayon parallelism across all CPU cores. No GIL, no interpreter overhead, no FFI call overhead hidden inside a _sys crate.

Safe

chematic's own ~180,700 lines of Rust (tokei-measured code lines, all 20 crates, 2026-08-21) contain zero unsafe blocks outside one file: 9 unsafe {} blocks plus 1 unsafe extern "C" FFI declaration, all in the optional native-inchi layer (below). No C++ heap corruptions. No segfaults from malformed SMILES input. No platform-specific build failures from -sys crates. The compiler enforces memory safety at every call site chematic itself wrote.

The native-inchi feature is the single opt-in exception — it vendors the IUPAC InChI C library (v1.07.5) for bit-exact standard InChI. All other chematic crates stay FFI-free and unsafe-free. This count is chematic's own source only, not its dependency tree — the optional depict feature (SVG/PDF/EPS rendering) pulls in a font/image-rendering stack (resvg/usvg/rustybuzz/tiny-skia/zune-jpeg) that is not unsafe-free; see the comparison table footnote below for a measured count.

Anywhere

Pure Rust compiles to wasm32-unknown-unknown natively — no Emscripten, no cmake, no clang. The npm package @kent-tokyo/chematic is 1.10 MB gzip (2.94 MB raw) — roughly 2.3× smaller than RDKit.js's RDKit_minimal.wasm (6.91 MB raw) on a like-for-like raw-size basis. One codebase runs on Linux, macOS, Windows, and in every browser.

Benchmarks & Validation

*LogP max Δ = 1.1×10⁻¹³ across 4,999 molecules — within float64 rounding error.
†Stereocenter count: ~99.96% vs legacy CalcNumAtomStereoCenters (a handful of molecules where chematic matches FindPotentialStereo and legacy under-counts); ~98.6% vs new-CIP FindPotentialStereo (cage/bridgehead molecules where both chematic and legacy correctly return fewer than the new oracle). chematic is calibrated between both extremes. This measures whether an atom is flagged as a stereocenter, not whether its R/S label is correct — see the next row.
‡CIP R/S label agreement measures, for atoms both oracles agree are stereocenters, whether the assigned R/S descriptor matches — a stricter, separate check from stereocenter count agreement above. This row is chematic's default assign_cip() path. The separate chematic-cip engine now reaches 99.38% raw / 99.64% oracle-stable (Milestone 4 gate closed) and is reachable opt-in via assign_cip_with_mode(mol, CipMode::Accurate) (Rust), Mol.cip_stereo(mode="accurate") (Python), or cip_assignments_accurate_json (WASM). No default path changed; this row's 96.30% is unaffected.

All numbers are reproducible with the scripts in this repo.
Full history → benchmarks/ · Methodology → validation/

Comparison with Other Cheminformatics Libraries

§ RDKit itself has no built-in MolFromMMCIF/mmCIF writer; mmCIF interop is done via separate third-party tooling (e.g. PDBe CCDUtils) layered on top of RDKit, not RDKit's own I/O surface.

† Default build only. The optional native-inchi feature adds a C-compiler dependency for the vendored IUPAC InChI C library (v1.07.5). This is about C/C++ FFI specifically — the depict feature below pulls in pure-Rust rendering crates, so it doesn't add a C compiler dependency even though it isn't unsafe-free (see ‡).

‡ chematic's own ~180,700 lines of Rust (tokei-measured, 2026-08-21): unsafe-free outside native-inchi's 9 FFI blocks (see "Safe" above) — a real, verifiable claim about code chematic wrote, and categorically different from RDKit/OpenBabel's C++ FFI unsafe (uncheckable by any compiler at that boundary) even where the raw count is comparable. It is not true of the full dependency tree: the optional depict feature (SVG/PDF/EPS rendering) pulls in resvg/usvg/rustybuzz/tiny-skia/zune-jpeg, pure-Rust crates that are themselves not unsafe-free — measured directly (unsafe fn/impl/trait/{ openings): tiny-skia 151, zune-jpeg 79, rustybuzz 14, image 8, fontdb 3, tiny-skia-path 3 (258 total in this set alone). chematic-py (pip install chematic) and the npm package both depend on chematic-depict directly, so this applies to both real-world install paths, not just an edge case.

JavaScript / TypeScript (WebAssembly)

1.10 MB gzip — roughly 2.3× smaller than RDKit.js's raw WASM. No Emscripten, no cmake. Drop-in for browser or Node.js.

npm install @kent-tokyo/chematic

import init, { parse_smiles, get_descriptors_json, tanimoto_ecfp4,
               generate_3d_minimized_pdb, enumerate_stereo_isomers_json,
               maxmin_picks_ecfp4_json } from '@kent-tokyo/chematic';

await init();

const mol = parse_smiles('CC(=O)Oc1ccccc1C(=O)O'); // aspirin
console.log(mol.molecular_weight(), mol.qed(), mol.lipinski_passes());

// All descriptors as a JSON object
const desc = JSON.parse(get_descriptors_json(mol));

// Fingerprint similarity
const caffeine = parse_smiles('Cn1cnc2c1c(=O)n(c(=O)n2C)C');
console.log(tanimoto_ecfp4(mol, caffeine));  // 0.26

// 3D coordinates, stereoisomers, diversity picking
const pdb = generate_3d_minimized_pdb(mol);
const isomers = JSON.parse(enumerate_stereo_isomers_json(parse_smiles('C(F)(Cl)Br')));
const picks = JSON.parse(maxmin_picks_ecfp4_json('["CC","c1ccccc1","CCO","CCCC"]', 2));

218+ exported functions (plus MolHandle/DepictOptions class methods, measured 2026-08-21) cover descriptors, fingerprints, 3D geometry, reactions (incl. retro_disconnect_json — single-step retrosynthetic disconnection), diversity picking, and SDF round-trips. See the full WASM API reference for all exports.

Crate Reference

cargo test --workspace --lib --quiet                                          # 3,912 tests, all passing (2026-08-21)
cargo test -p chematic-inchi --features native-inchi --test standard_inchi  # +16 IUPAC-exact InChI tests

Recent Development

v0.22.0 (2026-08-29): New WASM ensemble binding, canonicalization-hang fix, 3-membered-ring embedding fix

• chematic-wasm: new embed_ensemble_v2_json binding for chematic_3d::embed_ensemble_v2, mirroring the Python binding (Mol.conformer_ensemble_v2()) via the existing pipeline_v2.rs conventions (camelCase JSON keys, schemaVersion: 1 envelope) — purely additive
• chematic-smiles: canonical_smiles/canonical_atom_order could hang on molecules with several simultaneously-unresolved symmetric regions (issue #421) — the automorphism backtracking search had no internal step bound; fixed with an always-on step ceiling that safely falls back to "not proven automorphic" rather than searching unbounded
• chematic-3d: 3-membered rings (cyclopropane/epoxide/aziridine/thiirane) failed closed at the distance-geometry embedding stage — a generic angle bound was overwriting the correct, tighter bond-length bound for a ring-closing pair that's simultaneously "1-3" and directly bonded; fixed by skipping the angle bound for any already-bonded neighbor pair; strict-MMFF94 3D corpus 252/265 → 263/265
• Full details in CHANGELOG.md's [0.22.0] section

v0.21.0 (2026-08-27): McsConfig charge/isotope matching + typed timeout outcome, four correctness fixes

• chematic-smarts: McsConfig gains match_charge/match_isotope fields (mirroring the existing match_chiral_tag, default false) and a new McsOutcome enum (Exhaustive/TimedOut) via find_mcs_with_config_checked, reporting whether a timeout cut the search short rather than silently returning a possibly-non-optimal result — purely additive, find_mcs/find_mcs_with_config unchanged
• chematic-smarts: find_mcs's branch-and-bound search was incomplete — grow() only ever tried the first frontier atom with no way to exclude it and try another, silently missing a strictly larger common substructure in some cases (minimal repro: OC(N)N vs NC(N) returned 2 atoms instead of the true 3); fixed via standard include/exclude branch-and-bound
• chematic-chem: disconnect_metals left a dative-bond-derived formal charge unneutralized after severing the metal bond (issue #403) — 34/4999 molecules in RDKit's own bundled NCI Diversity Set holdout were non-idempotent; fixed by recomputing the affected atom's H count via valence inference immediately after disconnection; NCI holdout 34 → 0 failures, new 11-fixture metal-complex holdout added
• chematic-chem: normalize_zwitterion invented a proton on the negative atom of a permanently charge-separated group with no transferable proton anywhere (e.g. a diazo-N,N'-dioxide), silently changing the molecule's formula (issue #407) — fixed by gating the transfer on both atoms actually having a proton to move; dev-corpus residual 4 → 1 (the remaining one is unrelated, see issue #402/#415)
• chematic-chem: canonical_tautomer could produce a chemically invalid, over-valent nitrogen in a fused/bridged ring system (issue #415) — both aromatic H-shift mechanisms now validate their output via kekulization before accepting it
• Full details in CHANGELOG.md's [0.21.0] section

v0.20.1 (2026-08-26): Three canonical-SMILES/standardization correctness fixes (patch release, no breaking changes)

• chematic-smiles: coupled E/Z canonicalization could silently change geometry on re-canonicalization (issue #390) — two independent defects in the canonical writer's E/Z marker machinery, both required to reproduce the filed witness; fixed together, verified against a real 290-compound corpus (290/290 idempotent, 290/290 matching independent RDKit InChIKeys, up from 289/290)
• chematic-chem: standardize() silently dropped stereo tables on several rebuild paths (issue #399) — 8 functions in standardize.rs rebuilt the molecule via a bare MoleculeBuilder without carrying stereo_neighbor_order/bond_directions/stereo_groups forward, flipping @/@@ depending on ring-open/close role; dev-corpus standardize-path idempotency 615/519 → 68/60 (the exact pre-#392 baseline), NCI holdout (4,999 unused real molecules, run once) 0 stereo-related failures
• chematic-smiles: canonical-writer ring-closure bond markers ignored the closure partner's aromaticity (issue #395) — a genuinely non-aromatic ring-closure "fusion" bond between two individually-aromatic atoms (e.g. c1-2) silently became aromatic on re-parse; dev-corpus bare-parse idempotency 73/57 → 0/0, a complete fix, independent RDKit InChI oracle 0 mismatches across all 10,000 corpus lines
• Combined, the two standardize-path fixes bring that corpus to 0/4 residual — the 4 remaining failures are traced to two newly-filed, not-yet-fixed issues (#407, #402-class), not folded into this release
• Full details in CHANGELOG.md's [0.20.1] section

v0.20.0 (2026-08-25): Stereo-safe 3D generation, a connectivity-ordered coordinate engine, and identity-correctness fixes for remove_hydrogens

• chematic-3d/chematic-py/chematic-wasm: PipelineV2Config::stereo_safe(force_field_policy) — a single-call configuration that resolves a real gap for ring-fused declared stereocenters (testosterone, cholesterol, and similar), where repair_tetrahedral_center previously had no coordinate to reflect an implicit H against. Measured on a 29-molecule × 5-seed corpus: 144/145 (99.3%) correct_and_ok, 0 silently wrong, testosterone/cholesterol both 5/5 seeds on every declared stereocenter
• chematic-3d: generate_coords_connectivity_ordered, a new public alternative 3D placement engine (issues #256/#255) — places rings and chain atoms in true connectivity order rather than "all rings, then all chains." Measured: raw-geometry soundness 10/33 → 33/33 on a differential corpus with zero regressions, post-UFF bond-violation rate reaching 0.0000 (better than the legacy engine's own baseline). generate_coords itself is completely unchanged — ships as an available alternative, not a default-behavior switch; no existing caller is routed to it
• chematic-3d: rescue_with_distance_geometry_v2 (the UFF-catastrophic-blowup rescue bridge) now enforces declared chirality on retry (issue #210, partial fix) — zero regressions on its 58-molecule corpus, one of 5 named residual molecules newly succeeds; 4 residuals remain unfixed via this specific bridge (though resolved via stereo_safe above)
• chematic-chem: remove_hydrogens no longer destroys isotope-labeled hydrogen ([2H], [3H]) or silently drops declared stereo/E-Z information on every call — both were real, shipped correctness bugs found via a downstream consumer's 9.47M-compound real-world corpus scan, unaffected molecules confirmed unchanged, 289/290 of the originating investigation's identity mismatches resolved
• chematic-py: Mol.conformer_ensemble_v2(config) exposes embed_ensemble_v2 (deterministic multi-conformer generation, energy ranking scoped within force field, full per-attempt provenance) — added alongside the existing conformer_ensemble(), not replacing it. New best-of-10 benchmark arm confirms it works robustly at scale (~250/265 molecules, median RMSD 2.147 Å / TFD 0.344 vs. RDKit) — RDKit conformer-selection parity is a separate, unestablished claim
• Known limitations: generate_coords not yet routed to the new engine; issue #210's 4 residuals remain open via that specific bridge; issue #390 (a single-molecule E/Z correctness residual, unrelated) remains open; no fresh full-corpus re-measurement was run solely for this release
• Full details in CHANGELOG.md's [0.20.0] section

v0.19.0 (2026-08-23): Round 2C aromatic lactam/lactim tautomer fix, plus a benchmark/validation refresh

• chematic-chem: Tautomer & Parent Identity round 2C (ROADMAP.md Phase 2) — canonical_tautomer/tautomer_parent now cover the aromatic lactam/lactim class for 2-pyridone, 4-pyridone, uracil, cytosine, guanine, methylpyrimidinone, and the primary/N9-methyl hypoxanthine cases. Aromatic exocyclic tautomer edges are traversed in both directions by bounded enumeration, while canonical selection retains the lactam preference. The former tp2-39 and tp2-holdout-06 residuals were corrected after RDKit InChIKey review exposed positional-isomer fixture errors; the unrelated nitroso/oxime defect is fixed. Python/WASM Parent-API bindings are implemented.
• Benchmark/validation refresh: every number in docs/benchmark.md/docs/validation.md was pinned to chematic v0.4.29/RDKit 2026.03.3 (~14 releases stale) — re-measured fresh against RDKit 2026.03.4. The 4,999-mol accuracy corpus is now committed (scripts/chembl_accuracy_corpus_4999.smi, previously an uncommitted personal path); molecular weight has a real corpus-wide check for the first time (99.82%, not the previously-unmeasured "175-mol"/100% placeholder); CIP R/S/E/Z label agreement re-measured at 99.74–99.78% (up from a stale 96.30–96.83%); WASM bundle size rebuilt clean; the ECFP4 "diverse corpus" figure now has a reproducible source (benchmark_vs_rdkit.py --corpus, previously none existed); 3D conformer generation's "Good (ETKDG rules)" framing corrected to "Experimental," matching the migration guide's own honest characterization
• Full details in CHANGELOG.md's [0.19.0] section

v0.18.0 (2026-08-20): Python/WASM bindings for the 7 v0.17.0 formats, plus an MMFF94 atom-typing fix and a binding-quality/cross-language-consistency pass

• chematic-ff: fixed the aryl-isothiocyanate cumulated-double-bond CSP carbon mistyping from issue #337 (getTotalDegree() == 2 replacing a triple_bonds > 0-only check — a strict superset, RDKit's real rule); the other 6/8 molecules behind that issue were re-diagnosed as a genuine RDKit Kekulization/MMFF-aromaticity-perception artifact (confirmed via direct negative-control fragments) rather than a locally-fixable typing rule, and left as an honestly-disclosed residual
• chematic-py: Python bindings for all 7 v0.17.0 formats (mmCIF, PQR, ORCA, QCSchema, Gaussian Cube, OpenDX, LAMMPS data/dump) — previously Rust-only; VolumetricGrid/LammpsDumpFrame pyclasses with numpy-array properties, to_opendx/to_opendx_lossy fail-closed split preserved faithfully; a py.typed marker verified to actually ship in the built wheel (mypy --strict passes against a fresh-venv wheel install, not just the source tree)
• chematic-wasm: WASM (wasm-bindgen) bindings for the same 7 formats, plus 5 additive js_sys::Float64Array/Uint32Array-returning functions alongside the existing JSON-string API (large numeric grid/row data without a full JSON round trip) — this crate's first typed-array precedent
• Cross-language parity: the same 4 small fixtures (Cube, OpenDX, mmCIF, LAMMPS triclinic dump) independently verified to produce identical results from Rust, Python, and WASM entry points — no discrepancy found
• Full details in CHANGELOG.md's [0.18.0] section

v0.17.0 (2026-08-17): Format/Python/materials-interop breadth, plus two MMFF94 charge/bond-order accuracy fixes

• chematic-mol: square-planar (@SP1/@SP2/@SP3-equivalent) stereo read/write for MOL/SDF via 3D-coordinate-derived reperception; PDBx/mmCIF, PQR, QCSchema JSON, and ORCA input/output; CIF explicit symmetry-operation expansion into a full unit cell (Rust + Python); a shared VolumetricGrid type plus Gaussian Cube and OpenDX (APBS-scoped) I/O; LAMMPS data-file (read_data format) and dump/trajectory-file I/O as standalone document types, not integrated with Molecule
• chematic-py: new Python bindings for chematic-crystal's Lattice/PeriodicStructure/Site — found and fixed a real pre-existing bug along the way (to_cif() silently re-declared an unexpanded-symmetry CIF as false P1)
• chematic-ff: MMFF94 bond-order-classification fix (assign_mmff94_numeric_types_with_view — production energy/gradient entry points and the coverage gate now agree on classification; torsions_missing 257→0 on the 265-molecule Wave 1 corpus) and an MMFF94 BCI partial-charge fix (own wrong bond_type_for, then root-caused a second bug to RDKit's atom-type-derived formal charge never being computed at all) with one post-minimization stereo-repair addition the first fix surfaced. Production pipeline_v2_mmff94_strict: 240/265 → 241/265
• Release-hygiene: corrected an MSRV declaration that didn't match reality (rust-version raised to 1.88, now continuously verified by a dedicated CI job)
• Full details in CHANGELOG.md's [0.17.0] section

v0.16.0 (2026-08-15): Periodic-structure interoperability (CIF/POSCAR/FPS) and generalized stereochemistry foundation

• chematic-mol: new optional crystal feature bridges the existing CIF reader/writer to chematic_crystal::PeriodicStructure (parse_cif_periodic_structure/write_cif_periodic_structure) — cell parameters to Lattice, _atom_site_occupancy to Occupancy, disorder-sharing atom-site rows merged into one PeriodicSite's multi-species list. New CifSymmetryStatus enum distinguishes genuinely-P1 CIFs from CIFs that declared symmetry this parser doesn't expand, rather than silently treating the latter as P1. chematic-crystal itself remains independent of chematic-mol/Molecule (dependency direction is one-way: chematic-mol → chematic-crystal, optional)
• chematic-crystal: native POSCAR/CONTCAR (VASP structure format) read/write — parse_poscar/parse_contcar/write_poscar, VASP 5 only, both scale-factor conventions, Direct/Cartesian coordinates, selective dynamics, ion velocities, and CONTCAR's predictor-corrector MD-restart section preserved verbatim (VASP's own docs don't specify its numeric layout)
• chematic-fp: new fps module — streaming read/write for the FPS ("Fingerprint file format") text-based interchange format popularized by chemfp/OpenBabel, hex bit-ordering verified against the chemfp spec, reuses BitVec2048/BitVecN as the sole bit-vector representation
• chematic-core: new stereo_geometry module — stereo configuration modeled as a coordination geometry (Tetrahedral/SquarePlanar, #[non_exhaustive] for future TBP/octahedral) plus the equivalence class of ligand-slot permutations under that geometry's proper rotation group (A4, order 12, for tetrahedral; the order-8 S4-stabilizer of a trans-pair partition, not the naive order-4 in-plane-only group, for square-planar). Replaces two independent hand-written stereo-remapping algorithms in chematic-smiles; @/@@/@SP1/@SP2/@SP3 semantics fully preserved (88-fixture byte-identical canonical-SMILES regression). Fixed a real bug found along the way: a square-planar-tagged atom in chematic-3d could be silently coerced into a tetrahedral chiral-volume check decided by floating-point noise; also fixed a transient allene-end-carbon parity regression surfaced during development, pinned by an exact golden-value test.
• Release-grade re-measurement of the pipeline_v2 vs RDKit 2026.03.4 benchmark (superseding stale 2026-08-06 numbers): mmff94_strict 149/265 → 239/265. New finding: torsion parameter coverage, not bond/angle, is now the dominant remaining MMFF94 gap (71% of complete_bonded_term_gated failures cite missing torsion parameters, 0% OOP, 0% bonds) — direct evidence for the project's next MMFF94 roadmap item
• Full details in CHANGELOG.md's [0.16.0] section

v0.15.0 (2026-08-14): chematic-crystal — periodic (crystal) structure foundation crate, MMFF94 Bond/Angle empirical-rule fallback (issue #227)

• New crate chematic-crystal: periodic (crystal) structure representation and geometry — Lattice (triclinic-capable, validated matrix/inverse/reciprocal vectors), FractionalCoord/CartesianCoord, PeriodicSite/SiteSpecies/Occupancy (multi-species disorder-ready), and PeriodicStructure with exact (not round()-approximate) periodic minimum-image distance — equidistant periodic images resolve deterministically to the lexicographically smallest image — cutoff neighbor enumeration, and diagonal supercells. Deliberately not an extension of chematic_core::Molecule (a bond graph). Optional serde feature; optional crystal feature on the chematic facade, included in full (does not change default, which stays empty). No symmetry, no CIF parser changes, no Python/WASM/MCP bindings yet
• chematic-ff: ported Halgren's MMFF.V eq. 18-20 empirical Bond-stretch/Angle-bend rule (mmff94_bond_energy_resolved/mmff94_angle_energy_resolved, new additive functions — the existing mmff94_bond_energy/mmff94_angle_energy keep their original signatures), tried strictly after the existing exact-table/eqLevel-ladder lookup so it never overrides a real table hit. Along the way, found and fixed a real data gap: 97 rows present in RDKit's real Angle table (generic central-atom-type-only theta0 defaults) were missing from chematic's port. One triple is deliberately left unresolved (fails closed) rather than guessed — the outer atom type has no equivalence-class entry and RDKit's own real code dereferences that unchecked (undefined behavior), so its live-oracle answer couldn't be attributed to any well-defined mechanism. Also fixed 5 pre-existing MMFF94 atom-typing gaps and ported RDKit's eqLevel atom-type-equivalence ladder for Angle lookup. Net effect on the 265-molecule Wave 1 corpus (production minimization path), reported as two separately-verified numbers (both via a full per-molecule join, zero regressions either way): full v0.14.1→v0.15.0 change 158/265 → 248/265 (107 → 17 failing); the empirical-rule work specifically (isolated from the atom-typing/eqLevel prerequisites merged earlier in this same release) 178/265 → 248/265 (87 → 17 failing). The 3 molecules still MinimizationFailed in the final state were already non-Ok in v0.14.1 — a pre-existing geometry issue newly exposed once real parameters became available, not a regression
• Full details in CHANGELOG.md's [0.15.0] section

v0.14.1 (2026-08-12): Anticancer platinum coordination-chemistry compatibility fixes, Extended XYZ (extxyz) read/write

• chematic-core: valence_inferred_hcount treated a BondOrder::Dative bond's donor side exactly like a covalent single bond when computing implicit hydrogen count — an un-bracketed dative donor like N->[Pt]Cl computed as NH2 instead of the chemically correct NH3. Donor-side dative bonds now contribute 0 to the valence sum; found via a platinum coordination-chemistry benchmark but general (verified against Fe/Co/Pd/Ru acceptors too), not platinum-specific
• chematic-mol: MDL bond type 9 (dative/coordinate — RDKit's own V3000 convention for Bond::BondType.DATIVE) silently mapped to BondOrder::Single in both V2000 and V3000 readers, quietly discarding coordination-bond semantics on read. Both readers now map code 9 to BondOrder::Dative; V3000's writer now emits code 9 instead of collapsing to plain single
• chematic-chem: avg_mass/mono_mass covered only ~24 light main-group elements and silently fell back to atomic_number as f64 for every other element — every transition metal, lanthanide, actinide, and heavy post-transition element (platinum: atomic number 78, real mass ~195 Da, previously returned "78.0 Da") got a wildly wrong mass with no error. Extended to all 118 Element values, sourced from RDKit's periodic table data, with the ~24 previously-covered values kept as-is where they differ (selenium: this project's value is the current IUPAC standard, RDKit ships the superseded pre-2013 value)
• chematic-mol: new Extended XYZ (extxyz) format support — parse_extxyz/write_extxyz, ExtxyzReader/ExtxyzWriter, parse_extxyz_all, built as an extension of the existing multi-frame XyzFrame type (ASE's Lattice= cell matrix, typed per-atom Properties= columns, arbitrary key=value frame metadata); a plain XYZ file round-trips through the extxyz reader/writer unchanged. Python: from_extxyz/from_extxyz_all/to_extxyz. WASM: mol_from_extxyz/extxyz_frame_json/to_extxyz_json. Breaking (Rust API only): XyzFrame gained three public fields, XyzError gained seven variants, write_extxyz now returns Result<String, XyzError> — a real break to the chematic-mol v0.14.0 Rust API already published to crates.io, not merely an unreleased-API change
• Platinum coordination-chemistry stereochemistry (square-planar cis/trans identity, e.g. cisplatin vs. transplatin) remains unrepresented — measured and explicitly not fixed this release, see validation/platinum/FEASIBILITY.md
• Full details in CHANGELOG.md's [0.14.1] section

v0.14.0 (2026-08-11): Stereo-aware distance geometry — declared E/Z enforced as a bound-matrix constraint, enforce_chirality composable with post-minimization stereo verification, Python/WASM exposure

• chematic-3d: root-caused and fixed the issue #285 release-gate waiver from v0.13.0 — apply_vdw_bounds's generic non-bonded Van der Waals lower bound was being applied to a declared-E/Z alkene's own 1-4 substituent pair regardless of declared stereochemistry, structurally excluding the correct cis geometry from ever being sampled. New apply_declared_ez_bounds (enforce_chirality-only) intersects an analytic same-side/opposite-side 1-4 distance bound into the bond matrix before the generic Van der Waals floor applies, so the correct geometry is reachable by construction, not by post-hoc repair/retry/reflection. Unlike tetrahedral chirality (which a pairwise distance matrix can never encode — a molecule and its mirror image have identical pairwise distances), declared E/Z is genuinely distance-representable, since cis/trans are two different scalar separations, not mirror images. Measured on the 265-molecule corpus's declared-E/Z subset (39 molecules): stereo-satisfied 22 → 42, violated 23 → 3, pipeline success/soundness unchanged
• chematic-3d: embed_pipeline_v2's config-validation gate previously rejected enforce_chirality: true for any stereo_policy other than Ignore. Corpus measurement found this wrong — enforce_chirality protects embedding-time correctness only, and force-field minimization (which has no notion of declared stereo) can walk a correctly-embedded E/Z bond back across its boundary afterward (found on 2 real molecules, confirmed by re-running with no force field). enforce_chirality: true is now also allowed with StereoPolicy::VerifyOnly, whose existing post-minimization gate catches exactly this failure mode as a typed error instead of a silent wrong-stereo success
• chematic-py, chematic-wasm: enforce_chirality (default false) is now a real, settable parameter/field on PipelineV2Config/PipelineV2Config.safe() (Python) and the enforceChirality JSON field (WASM) — neither binding had ever threaded the field through before, so the fix above was previously unreachable from Python or WASM callers
• chematic-rxn: fixed suzuki_biaryl's retro-template (issue #294) — [c:1][c:2] never matched a real biaryl bond, only intra-ring aromatic bonds, since two adjacent aromatic atoms with no explicit bond token default to aromatic in this crate's SMILES convention. Fixed to [c:1]-[c:2]. Found along the way: 14 of 59 DEFAULT_TEMPLATES entries silently never parse at all — filed as issue #296, not fixed here
• Opt-in only — enforce_chirality: false remains the default everywhere; the default conformer path (generate_coords_etkdg/Mol.conformer_ensemble()) is untouched
• Full details in CHANGELOG.md's [0.14.0] section

v0.13.0 (2026-08-10): MMFF94 stretch-bend + torsion parameter-selection parity (both breaking), per-atom stereocenter API, E/Z completeness, macrocycle detection, notation-invariant atropisomer detection/assignment, XYZ I/O

• chematic-ff: mmff94_stbn/mmff94_stbn_type_only now key the MMFF94_STBN table lookup on RDKit's real, finer-grained "stretch-bend type" (getMMFFStretchBendType, 0-11) instead of the coarser angle type (0-8) previously used as a stand-in (issue #227) — 220 of 427 stretch-bend routing candidates on the 265-molecule Wave 1 corpus move from RDKit's generic Dfsb periodic-row default to the correct, specific parameter; angle_type_for's ring-offset formula also corrected to match RDKit's real getMMFFAngleType. Breaking: mmff94_stbn/mmff94_stbn_type_only's leading u8 parameter is now stretch_bend_type, not angle_type — same shape, different required value; use the new pub stretch_bend_type_for to compute it
• chematic-ff: torsion_type_for now classifies from the real j-k bond's MMFF bond type (reusing bond_type_for) plus RDKit's real local-bond-adjacency ring-4/5 override, instead of atom-type-membership alone — corrects 76.9% of the 1,107 previously-missing torsion instances via classification alone, and, corpus-wide, corrects 1,792 of 13,530 torsion instances that resolved to a silently wrong parameter value before (not just missing coverage) — 99.1% of the corrected values independently confirmed against a live RDKit oracle, 0 newly lost. Breaking: torsion_type_for's signature changed from (rings, i, j, k, l, tj, tk) to (mol, i, j, k, l, ti, tj, tk, tl)
• chematic-mol: XYZ / multi-frame XYZ read-write (parse_xyz/write_xyz, XyzReader/XyzWriter) — explicit hydrogens kept as real atoms, no connectivity/bond-order inference, fails closed on atom-count mismatch or non-finite coordinates
• chematic-perception: stereo_centers(&Molecule) -> Vec<(AtomIdx, bool)> exposes per-atom tetrahedral-stereocenter classification (issue #263), previously only available as an aggregate count; fixed two bugs found while adding it — a u64 overflow for negatively-charged atoms in the shared Morgan-rank helper (issue #267), and an implicit-hydrogen rank-0 sentinel colliding with a real atom's normalized rank 0 that silently dropped genuine specified stereocenters
• chematic-chem: ez_completeness(&Molecule) -> EzCompleteness (issue #264) reports specified/unspecified/total declared E/Z double bonds, matching RDKit's own stereo-bond-eligibility rules (terminal/symmetric bonds excluded, ring bonds <8 atoms excluded via BFS shortest-cycle, not SSSR alone — correctly handles bridged-bicyclic cases like norbornene)
• chematic-chem: detect_atropisomers/assign_atropisomer_chirality are now fully notation-invariant (issues #262, #276) — detection is SSSR-based (two aromatic carbons in separate rings, both with ortho substitution) rather than keyed off whether the SMILES wrote the inter-ring bond explicitly or left it implicit; chirality assignment's own redundant bond-order gate is now aligned with detection's own classification instead of re-deriving a separate, notation-sensitive check
• chematic-perception: is_macrocycle(ring: &[AtomIdx]) -> bool (issue #266) — a single shared ≥9-atom-ring predicate, replacing duplicated hardcoded thresholds in chematic-3d
• v0.13.0 release-gate note: 2 of 265 Wave 1 corpus molecules (chembl_tier_b_0126/0168) show a 1-stereocenter-satisfaction regression, root-caused to a pre-existing distance-geometry embedding defect (present since v0.12.0) that used to be accidentally masked by the now-fixed torsion classification bug — confirmed via RDKit's own MMFF94, given identical starting coordinates, exhibiting the same behavior. Shipped under an explicit waiver (issue #285); not a new defect introduced by this release's MMFF94 fixes
• Full details in CHANGELOG.md's [0.13.0] section

v0.12.0 (2026-08-09): MMFF94 stretch-bend production fix (breaking), 3D starting-geometry fix for fused/multi-ring molecules

• chematic-ff: mmff94_stbn now falls back to RDKit's real 29-row periodic-table-row stretch-bend defaults when the specific/generic MMFF-type table has no row — unconditional production behavior for every MMFF94 policy, not behind an opt-in flag. Missing stretch-bend instances on the 265-molecule Wave 1 corpus: 2,107 → 0. Breaking: mmff94_stbn gained 3 required atomic_num_{i,j,k}: u8 parameters (prior type-only behavior kept as new mmff94_stbn_type_only); Python's raw PipelineV2Config(...) constructor gained a new required gate_mmff94_stretch_bend argument (.safe(...) unaffected)
• chematic-3d: dg::generate_coords no longer produces atom-coincident or wildly-stretched starting geometry for several multi-ring topologies (issue #185/#252) — root/ring-vertex collision, ring-fusion-order mismatch, and fixed-offset ring-island anchoring were all independent bugs, not a UFF minimizer defect as issue #185 originally suspected. All 28 MinimizationFailed cases on the 265-molecule corpus now resolve to Ok, 0 regressions. Two known, separately-tracked residual limitations remain unfixed: fused-ring seam orientation (issue #255) and chain-bridged ring islands (issue #256)
• Full details in CHANGELOG.md's [0.12.0] section

v0.11.0 (2026-08-04): MMFF94 O2CM typing coverage, SMIRKS/CDXML stereo correctness, 2D/3D layout fixes

• chematic-ff: closed the O2CM terminal-oxygen typing gap (issue #227 Priority 1A-3) — atom-type parity 98.82% → 99.37% on the 265-molecule Wave 1 corpus, oxygen-element parity 95.88% → 100%, strict-gate minimization success 123 → 130/265, 0 cross-element mismatches (unchanged). Issue #227 stays open
• chematic-rxn: SMIRKS product chirality assignment made parity-aware — a reordered mapped template neighbor order now correctly inverts/validates the product's @/@@ flag instead of copying it verbatim; inherited (non-template) chirality now fails closed to Chirality::None when its neighbor order or mapped topology can't be validated
• chematic-mol: CDXML reader now perceives tetrahedral stereo from directional wedges (RDKit issue #9359), wired into the same shared mechanism MOL/MRV already use; non-directional Bold/Hash/Dash displays are opt-in via CdxmlParseOptions and, when enabled, invariant to CDXML's B/E bond-atom ordering
• chematic-depict: independent (non-fused) ring systems no longer collide at identical/near-identical 2D coordinates
• chematic-3d: ETKDG macrocyclic amide 1-4 distance bounds now split by true cis/trans ring-continuation role instead of blanket-pinning all four combinatorial pairs to cis; abstains to a relaxed band when a central amide bond is shared by multiple eligible macrocycles at once
• Full details in CHANGELOG.md's [0.11.0] section

v0.10.1 (2026-08-02): MMFF94 numeric-typing correctness hotfix

• chematic-ff: fixed a class of bug where MMFF94 could silently resolve an atom against a parameter row belonging to a different element and report the resulting physically-wrong energy as success (issue #227's "furan collision") — the aromatic atom typer never implemented RDKit's real 5-/6-ring alpha/beta-heteroatom classification. Ported from a pinned RDKit source with a new provenance-cited numeric-type registry, plus a construction-time semantic-compatibility invariant that makes this bug class fail closed (NumericTypeError) instead of silently wrong, going forward. That invariant caught two more instances of the identical bug: a protonated amine N and an anionic O were each being typed as the other element's parameter row. Measured on the 265-molecule Wave 1 corpus (production API): 44 → 102 successful MMFF94 minimizations, 0 cross-element type mismatches across 6693 comparable atoms vs. a pinned RDKit oracle (91.83% exact match)
• This is a correctness hotfix, not a coverage-completion release — issue #227 stays open (140 MissingParameters and 22 MinimizationFailed cases remain, stretch-bend is not yet gated, no full-corpus energy/gradient parity harness exists yet). See Migration notes in CHANGELOG.md's [0.10.1] section if you cache MMFF94 results
• Full details in CHANGELOG.md's [0.10.1] section

v0.10.0 (2026-08-01): Match-level SMIRKS reaction application, MRV 2D stereo, shared E/Z carrier bond fix

• chematic-rxn: find_reaction_matches/apply_reaction_match (issue #225) — a public seam between enumerating a SMIRKS's matches against reactant molecules and applying one of them, for callers that need to accept some matches and reject others (e.g. based on whether the matched bond is a ring bond) without discarding the whole run_reactants call. run_reactants/run_reactants_strict are now implemented in terms of these two functions, unchanged in cost (still one SMIRKS parse + one VF2 match pass per call)
• chematic-mol: MRV reader now perceives 2D wedge/hash tetrahedral and E/Z stereo (issue #202) — parse_mrv previously read wedge/dash bonds and 2D coordinates into coords_2d but never converted them into Atom.chirality/bond E/Z direction, silently dropping stereochemistry present in the file
• chematic-smiles: shared E/Z carrier bonds now resolved via a joint component solver (issue #149) — 10 of 18 previously-abstained fixtures become fully permutation-invariant; the remaining 8 are a documented, RDKit-verified semantically-safe residual (endocyclic double bonds in 5-/6-membered rings, where marker choice has no free degree). Issue #149 stays open pending a scoped fix for the ring-constrained residual
• Full details in CHANGELOG.md's [0.10.0] section

v0.9.0 (2026-08-01): Opt-in 3D embedding pipeline v2 in Python + WASM, WASM-portable monotonic clock

• chematic-py: Mol.embed_pipeline_v2(config) — Python binding for the Rust-only pipeline_v2::embed_pipeline_v2 (torsion-knowledge-aware distance geometry + stereo verification/repair + policy-gated force field), returning full per-stage evidence (never just final coordinates) and a typed PipelineV2Error with structured, diagnostic-only partial evidence on failure. Applies directly to the caller's own atom order — no canonicalize/reparse. Additive; no existing default 3D API changed
• chematic-wasm: embed_pipeline_v2_json(mol, configJson) — WASM mirror of the above, same config/evidence shape as a tagged-union JSON envelope. New CI job builds both wasm-pack targets (nodejs/web) and runs the Node integration suite on every push/PR — this repo had zero WASM-runtime CI coverage before this
• chematic-3d/chematic-smarts: fixed std::time::Instant::now() panicking unconditionally under real wasm32-unknown-unknown (issues #219, #221) — the pipeline v2 binding's own first real-runtime run is what surfaced this pre-existing gap. Fixed via a small crate-internal clock module (web_time::Instant on wasm32, std::time::Instant elsewhere) in each affected crate; no chemistry/geometry/torsion/force-field or timeout-contract change
• chematic-3d: generate_and_minimize_uff() deprecated (issue #204) — it never ran chematic-ff's real UFF despite its name; kept, not removed, not behavior-changed
• Full details in CHANGELOG.md's [0.9.0] section

v0.8.1 (2026-07-30): canonical_smiles() explicit/implicit hydrogen-count correctness fix

• chematic-smiles/chematic-core: two representations of the same molecule that differ only in whether an atom's H count came from bracket notation ([Cl]) or organic-subset notation (Cl) — when the explicit value merely repeats what valence inference gives anyway — now canonicalize identically. Some canonical SMILES output strings for existing inputs will change as a direct, intended consequence — see CHANGELOG.md's [0.8.1] Migration notes if you depend on exact string stability across versions
• Full details in CHANGELOG.md's [0.8.1] section

v0.8.0 (2026-07-29): Opt-in fail-closed 3D embedding pipeline, canonical-SMILES automorphism-orbit pruning

• chematic-3d: new opt-in pipeline_v2::embed_pipeline_v2 — stochastic distance geometry + torsion knowledge + stereo verification/repair + typed force-field minimization in one 12-stage pipeline, with a fail-closed stereo re-check after minimization. Existing default behavior is unchanged
• chematic-smiles: fixed the canonical_smiles() performance regression reported by RENKIN (~5x geomean speedup on high-symmetry molecules); also fixes a Dative-bond round-trip bug (issue #194)
• Full details, benchmark numbers, and known limitations in CHANGELOG.md

Full version history back to v0.1 — every release, corpus-level before/after numbers, root causes, and migration notes — is in CHANGELOG.md.

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Reliability by Feature

Not all features have the same validation depth. This table tells you what to trust.

Full benchmark methodology → validation/ · History → benchmarks/

Known Limitations

• canonical_smiles() is now partially normalized for E/Z stereochemistry — still not safe as a dedup or cache key. Isolated/simple E/Z double bonds have two equally correct //\ spellings (e.g. /N=N/ vs \N=N\); the writer previously never normalized between them. Fixed for the general case: every connected E/Z system (a double bond plus every directional bond geometrically tied to it, including whole conjugated chains) is now normalized so its first directional bond in canonical write order is always /, regardless of input spelling. Measured on the 5,000-mol ChEMBL corpus, worst-of-10: E/Z-only self-instability (tetrahedral stereo stripped) improved 9.76% → 5.50% (275/5000 still unstable); structural correctness unaffected by this change (re-verified 0/5000 ChEMBL and 0/33 acyclic-polyene corpus). The residual 275 are confirmed 100% cosmetic — every unstable case's variants represent the same molecule per RDKit, zero corruption — but the cause is a mixed pool, not fully root-caused: about half match a specific motif (a small ring bearing two or more exocyclic double bonds, e.g. cross-conjugated cyclic diimines) where which physical bonds count as "one system" is not yet input-spelling-invariant; the other half is uncharacterized. Until this closes fully, ~1 in 18 stereo-bearing molecules (down from ~1 in 10) can still produce two different, individually valid canonical_smiles() strings for the same molecule — do not use it as a dedup or cache key today; document your own dedup key as apply_aromaticity()-normalized in the meantime if this matters for your use case.
• Canonical SMILES structural corruption — fixed. Before this fix, canonical_smiles(parse(x)) could silently emit a different stereoisomer (not just a differently-spelled but equivalent string) depending on x's input traversal order. Measured on a 5,000-mol ChEMBL subset, worst-of-10 independently-traversed representations per molecule, RDKit-verified structural correctness: 4.28% (214/5000) of molecules had at least one variant round-trip to the wrong molecule. Root-caused to two independent parser bugs (not the originally-suspected "conjugated double-bond markers are geometrically coupled across bonds" — that diagnosis was disproven, see below), each confirmed via a real found molecule and a minimal regression test: (1) a ring-closure directional-bond (//\) marker read at the closing occurrence of a ring digit was stored raw instead of flipped to the opening→closing sense, corrupting a conjugated E/Z chain whenever its connecting bond happened to be routed through a ring closure; (2) a stereocenter that opens a ring whose partner closes inside its own branch had its neighbor-order resolution keyed by the reusable ring digit rather than a unique per-occurrence id, so a later, unrelated reuse of the same digit elsewhere in the SMILES could silently steal and corrupt the stereocenter's neighbor order. After both fixes: structural correctness is 100% (0/5000) on ChEMBL, confirmed three times over via independently-ordered reconstructions of the fix (with and without an unrelated third ranking fix, to rule out a hidden dependency). Because both root causes are ring-closure-specific — and retinoids, carotenoids, prostaglandins, leukotrienes, and polyene macrolides carry their long conjugated systems in acyclic chains, essentially absent from ChEMBL-random sampling — this was independently re-verified on a dedicated 33-compound corpus of exactly those classes (tretinoin, β-carotene, lycopene, amphotericin B, leukotriene B4, and 28 others; scripts/polyene_corpus.csv): 0/33 (0.00%) at worst-of-30, with a positive control confirming 12/33 (36.36%) corruption on the pre-fix code for this same corpus (all 12 failures were ring-closure-heavy structures; zero purely-acyclic examples — including fully acyclic lycopene — ever failed, even unpatched). This directly disproves the original "any conjugated chain" diagnosis and closes the investigation with no remaining corruption class identified. Skeleton-only and tetrahedral-only self-stability also reached 0% (were 0.16% and 4.36%); raw combined self-stability (all stereo intact) improved 86.02% → 90.28% (13.98% → 9.72% unstable) — the entire remainder is the separate, non-corrupting direction-normalization gap described above, not residual corruption. Round-trip invariance (canonical(parse(canonical(m))) == canonical(m)) improved slightly, 98.26% → 98.32%, since it was never measuring the corruption class directly.
• Ring perception (SSSR) was non-deterministic and non-minimal — fixed. The old find_sssr built a single spanning tree and took one fundamental cycle per non-tree edge, with no redundancy to recover a smaller ring when the tree's shape made one unnecessarily large (naphthalene, c1ccc2ccccc2c1, deterministically returned ring sizes [6, 10] instead of [6, 6]). find_sssr now uses Horton's algorithm (candidate cycles from every vertex × every edge via shortest-path trees, O(V·E) candidates, canonical-rank tie-break for determinism), giving a genuinely minimum-weight, deterministic basis. Measured on a 5,000-mol ChEMBL subset, worst-of-10 independently-traversed representations per molecule: self-stability 100% (was 50.6%); single-parse ring-size agreement with RDKit 98.9% (was 72.4%) — the residual ~1.1% gap is RDKit's own GetSymmSSSR legitimately returning more rings than the topological minimum for symmetric fused systems (e.g. cubane: μ=5, RDKit=6), not a chematic bug; full symmetrization (Vismara relevant cycles) is future work, not required for correctness. Downstream wins, same corpus: ring-size SMARTS [r5]/[r6] 0% instability (was 29–55%), NumAromaticRings 0% (was ~4%), RingCount/MW/TPSA/HBA/HBD/LogP/MR unaffected (were already 0%). Two known-narrow exceptions where the old SSSR bug had accidentally compensated for a separate, still-open aromaticity bug — see the Aromaticity model bullet below. Full methodology: scripts/ringinfo_parity.py.
• Murcko scaffold: ring topology and normalized string output are now fully stable. The previously-reported "100% traversal-order instability" was itself a measurement-harness bug (comparing Mol objects by Python identity instead of value — always reported "unstable" regardless of the real result); that script bug is fixed (scripts/ring_collateral_damage.py). Re-measured on a 5,000-mol worst-of-10 run after the canonical-SMILES corruption fixes above: after normalizing (apply_aromaticity().canonical_smiles_mode("nostereo")), self-stability is 100% (0/5000 unstable), down from a 0.8% residual — confirming that residual was the same canonical-SMILES structural corruption, not a Murcko ring-selection bug, and it is now fully resolved. Raw isomeric scaffold().smiles string comparison (no normalization) is 79.30% stable (20.70% unstable, was ~45%, essentially unchanged by the partial E/Z-normalization fix above — scaffolds strip most of the side-chain motifs that fix improves) — the remainder is the still-partially-open, non-corrupting //\ direction-normalization gap described above, not a scaffold-specific issue. scaffold() extracts the correct ring system reliably; compare via mol.apply_aromaticity().canonical_smiles_mode("nostereo") rather than raw .smiles if you need string equality across differently-ordered input.
• Aromaticity model: chematic applies Hückel 4n+2 per SSSR ring independently; RDKit uses fused-ring electron delocalization. Visible differences in N-heterocycles (pyridone, quinolone, indolizine). Current benchmark on 4,999-mol ChEMBL subset: HBA/HBD/aromatic ring count 100%; TPSA 100% (±0.1 Ų); LogP 100% (±0.01). Aromaticity-flag parity on Kekulized input measured worst-of-10-representations: 96.3% (scripts/aromaticity_atom_parity.py) — bit-for-bit unchanged by the SSSR fix above, confirming the SSSR bug and the aromaticity gap are independent; the aromaticity gap is root-caused separately to an aromatic_context bypass mechanism, not yet fixed. Two molecules (azulene, purine) are known to have regressed by the SSSR fix specifically — the old, broken SSSR had accidentally been masking the aromatic_context bug for these non-alternant/bridgehead-heavy structures. They are not present in the 5,000-mol measured corpus at all (confirmed by direct search — ChEMBL-derived drug-like corpora don't contain bare azulene/purine), so the 96.3% figure is unchanged because it cannot see them, not because they have zero impact; both are pinned as #[ignore]d regressions in chematic-perception's test suite with the root cause documented in-code, pending the aromatic_context fix.

Repository Structure

chematic/
├── Cargo.toml                    workspace root (v0.25.0)
├── CHANGELOG.md
├── crates/
│   ├── chematic-core/            Atom, Bond, Molecule, Element, kekulization (4-pass + blossom)
│   ├── chematic-smiles/          OpenSMILES parser/writer, canonical SMILES
│   ├── chematic-perception/      SSSR, 2-pass Hückel aromaticity, CIP stereo
│   ├── chematic-smarts/          SMARTS parser, VF2 subgraph isomorphism, MCS, LRU cache
│   ├── chematic-chem/            190+ descriptors, pKa, ADMET, BOILED-Egg, QED, SA Score,
│   │                             PAINS/Brenk filters, scaffold, standardization, BRICS/RECAP
│   ├── chematic-fp/              ECFP/FCFP, MACCS, MAP4, AtomPair, Torsion, MHFP, ERG
│   ├── chematic-ff/              MMFF94 full stack (7 terms), DREIDING, L-BFGS minimizer
│   ├── chematic-3d/              ETKDG, MD, SASA, USR shape screen, WHIM, GETAWAY, XYZ/PDB I/O
│   ├── chematic-depict/          2D SVG rendering, grid layout, CPK colors, highlighting
│   ├── chematic-rxn/             Reaction SMILES/SMIRKS, RunReactants, RECAP/BRICS
│   ├── chematic-mol/             SDF/MOL V2000+V3000, CML, CDXML parser/writer
│   ├── chematic-inchi/           InChI/InChIKey (pure-Rust approx + IUPAC-exact via native-inchi)
│   ├── chematic-iupac/           IUPAC name generation (25+ compound classes)
│   ├── chematic-mcp/             MCP server — 20 AI-callable tools (JSON-RPC 2.0 over stdio)
│   ├── chematic-wasm/            218+ WASM exports → npm @kent-tokyo/chematic
│   ├── chematic-py/              PyO3 Python bindings → pip install chematic
│   ├── chematic-ewald/           PME Ewald summation, B-spline interpolation
│   ├── chematic-crystal/         Periodic crystal structures: lattice, PBC, neighbors, supercells, POSCAR/CONTCAR I/O (not Molecule)
│   └── chematic/                 Umbrella crate with feature flags
├── demo/                         Interactive WASM playground (→ /playground/ on GitHub Pages)
│   ├── index.html
│   └── pkg/                      Pre-built WASM bundle (rebuilt on each release)
└── docs/                         MkDocs documentation site source
    ├── cookbook.md
    ├── getting_started/
    └── api/

Development Commands

cargo build --workspace                                                   # build all crates
cargo test --workspace --lib --quiet                                      # 3,912 lib tests
cargo test -p chematic-inchi --features native-inchi --test standard_inchi  # +16 InChI tests
cargo clippy --workspace -- -D warnings                                   # lints (zero warnings)

Citation

If you use chematic in academic or research work, please cite:

@software{chematic,
  author    = {kent-tokyo},
  title     = {chematic: A pure-Rust cheminformatics toolkit},
  url       = {https://github.com/kent-tokyo/chematic},
  version   = {0.25.0},
  year      = {2026},
}

License

Licensed under either of Apache License 2.0 or MIT License, at your option.

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