tabkit

Tabular files → schema + sample rows. The shared spreadsheet reader Tauri / Iced / native desktop apps reach for when they need to introspect XLSX / CSV / TSV without inventing the same calamine- plus-type-inference glue twice.

Status: v0.4 — API stability candidate for 1.0. Format coverage closed in v0.3 (XLSX-family + CSV/TSV + Parquet, with typed Date / DateTime cells). v0.4 freezes the public surface — see the stability section below for what's locked in. v0.4.x will iterate on examples + cookbook docs. 1.0 ships once the API is exercised by at least one downstream production user.

Why this exists

Every "show the user what's in their spreadsheet" project rebuilds the same calamine wrapper, the same type-inference pass, the same first-row-is-headers guess, the same ragged-row padding. Every project gets it slightly wrong:

• Treats Excel's Float(1.0) as a Float, so a qty column that should infer to Integer ends up as Float in the schema.
• Forgets ragged rows, hands downstream code a Vec<Vec<_>> where rows have different lengths.
• Hard-codes , as the delimiter, breaks on .tsv.
• Reads the entire file into memory chasing a 'sample.'

tabkit ships these bits once, with the edge cases handled in one place. It's deliberately lower-level than a full data tool — it hands you a [Table] and gets out of the way. Pair it with scankit for walk-and-watch and mdkit for documents → markdown.

Quick start

use tabkit::{Engine, ReadOptions};
use std::path::Path;

let engine = Engine::with_defaults();
let table = engine.read(
    Path::new("/Users/me/data/sales.xlsx"),
    &ReadOptions::default().max_sample_rows(10),
)?;

for col in &table.columns {
    println!("{} : {:?}", col.name, col.data_type);
}
for row in &table.sample_rows {
    println!("{row:?}");
}
# Ok::<(), tabkit::Error>(())

Design principles

1. Do one thing well. Read tabular files → return Table. Anything richer (SQL, persistence, change tracking) is the consuming application's job.
2. Send + Sync everywhere. A single Engine shared across threads, a single Reader instance per format.
3. JSON-friendly output. Value has six narrow variants so the result serialises cleanly through Tauri IPC. Dates flatten to Text for now — a future dates feature could carry typed dates.
4. Forward-compat defaults. Table, Column, Value, Error, and ReadOptions are #[non_exhaustive] so we can add fields / variants without breaking downstream callers.
5. Honest dep budget. calamine + csv + thiserror are the only required deps. ~1 MB compiled with both default backends.

Feature flags

Stability (v0.4+) {#stability-v04}

v0.4 is the API stability candidate for 1.0. The following surface is committed to and will only change with a major version bump:

• The Reader trait shape — required methods, default implementations, Send + Sync bound. Future trait methods land with default impls so existing implementors don't break.
• Engine construction + dispatch — new, with_defaults, register, read, len, is_empty.
• Table, Column, Value, DataType, Error, ReadOptions field/variant sets. All #[non_exhaustive] so we can grow them without major bumps. Pattern-matchers must include a wildcard arm.
• Feature flag names: calamine, csv, parquet, full. Each reader's per-format extension list is also stable.
• Per-reader name() strings ("calamine", "csv", "parquet").

The following are implementation details and may change in minor versions:

• Internal layout of any specific reader (private fields, helper methods, type-inference heuristics).
• Exact set of Table.metadata keys per backend (new keys may appear; documented keys stay).
• Auto-registration order in Engine::with_defaults (the rule "first registered wins for overlapping extensions" stays; the specific order doesn't).

1.0 will be cut once the API is exercised by at least one downstream production user.

Composing with DuckDB {#composing-with-duckdb}

When you need SQL queries on tabular data, use duckdb directly — DuckDB has excellent native readers for CSV and Parquet, and it's purpose-built for this. Use tabkit for "what's in the file" (schema, samples, type inference for the UI / agent grounding); use DuckDB for "compute over the data" (joins, aggregates, projections):

// 1. tabkit for schema + samples (fast, lightweight)
let table = tabkit::Engine::with_defaults().read(path, &Default::default())?;
println!("columns: {:?}", table.columns);

// 2. DuckDB for the SQL surface (when you actually need it)
let conn = duckdb::Connection::open_in_memory()?;
let path_str = path.display();
conn.execute(
    &format!("CREATE TABLE t AS SELECT * FROM read_csv_auto('{path_str}')"),
    [],
)?;
let mut stmt = conn.prepare("SELECT region, SUM(amount) FROM t GROUP BY region")?;
// ...

Same composition shape works for XLSX (read with calamine, write intermediate CSV/Parquet, query with DuckDB) and Parquet (DuckDB reads natively).

License

Dual-licensed under MIT OR Apache 2.0 at your option. SPDX: MIT OR Apache-2.0.

Status & roadmap

• v0.1 — schema + samples. Engine + Reader trait + Table + Column + Value, calamine + csv backends, type inference (Bool / Integer / Float / Text / Unknown), header-or-not, sheet selection for multi-sheet XLSX, ragged row padding.
• v0.2 — parquet feature. Apache Parquet read support via the parquet crate (default features off — no Arrow runtime). Same schema-and-samples surface, same type- inference rules.
• v0.3 — typed dates. Value::Date(String) / Value::DateTime(String) with ISO-8601 string payloads (no chrono dep). All three readers emit typed dates for source values that carry date semantics. Value is now #[non_exhaustive] for forward-compat.
• v0.4 — audit pass + 1.0 candidate. Stability commitments doc in lib.rs + README. #[non_exhaustive] already on every public struct + enum (added incrementally v0.1 → v0.3); #[must_use] already on every constructor + builder + accessor. Documentation-only release — no API- shape changes.
• v1.0 — once exercised by at least one downstream production user. Sery Link is the canonical integration target; v1.0 ships once the API survives real use without breaking changes.

Why no duckdb feature

Earlier roadmaps mentioned a v0.x duckdb feature for SQL queries on top of any read table. We dropped that plan because:

1. Dep weight. The bundled duckdb crate is ~50 MB compiled — tabkit's current ~4 MB would 13× by adding it. That violates the "small focused kit" aesthetic.
2. Scope creep. tabkit's contract is "schema + samples from a file." SQL queries are a fundamentally different abstraction: compute over data, not introspect a file.
3. DuckDB has native CSV/Parquet readers. A tabkit-DuckDB feature would duplicate functionality — users would have two readers for the same format and not know which to pick.
4. Composition is cleaner. See the next section.

Issues, PRs, and design discussion welcome at https://github.com/seryai/tabkit/issues.

Used by

tabkit was extracted from the schema-extraction layer of Sery Link, a privacy-respecting data network for the files on your machines. If you use tabkit in your project, please open a PR to add yourself here.

The kit family

tabkit is part of a coordinated suite of focused single-purpose Rust crates extracted from Sery Link:

• mdkit — documents → markdown (PDF, DOCX, PPTX, HTML, IPYNB, OCR).
• scankit — walk + watch directory trees with exclude-glob and size-cap filters.
• tabkit — spreadsheets → schema + sample rows (this crate).

Use them together, use them separately. The trait surfaces are designed to compose without forcing a particular runtime.

Acknowledgements

• calamine — tafia's industry-standard Rust XLSX/XLS/ODS parser. Does the heavy lifting for the calamine feature.
• csv — BurntSushi's battle-tested CSV reader. The fast path for CSV/TSV.