axon-lang

AXON — the formal cognitive language: a deterministic, proof-carrying AI runtime.

AXON is a programming language for AI cognition in which the properties you care about — this endpoint may not leak regulated data, this agent may not exceed this budget, this credential may not outlive this session — are type errors, checked before anything runs, rather than conventions enforced by code review.

The crate publishes as axon-lang; the library import is use axon::*.

The language reference, the design papers and the full documentation live in the repository README. This page is the crate's landing page: what you get, how to install it, and how to watch it refuse something.

Install

cargo install axon-lang

This installs axon — the compiler and governance CLI. It is what you want in CI, in a pre-commit hook, and on a developer machine: axon check needs no database, no HTTP server and no API key.

If the build stops with a cc/linker error rather than a Rust error, the C toolchain is what is missing.

Running governed flows: axon-server

axon compiles and audits; axon-server executes. It is a separate binary behind a feature flag, the way psql and postgres — or docker and dockerd — are separate:

cargo install axon-lang --features server            # adds `axon-server`
cargo install axon-lang --features server,postgres   # …with the SQL data plane

Both binaries are AGPL and both live in this crate. The split is a role boundary — compiler vs runtime — not a paid one.

Nothing disappears when you install less. Every subcommand stays in --help under every profile, and one whose feature is absent refuses in writing with the exact command that brings it back:

$ axon serve
X `axon serve` requires the `server` feature - this build was compiled without it…
  Reinstall with: cargo install axon-lang --features server
  and run `axon-server` (the `axon` you have keeps working for everything else).

axon check type-checks a program that declares backend: postgresql even in a build with no database driver — the compiler resolves a declaration; it opens no connection.

What the split costs and buys (measured 2026-08-06, warm registry, cold target dir): the default install is 11m09s → 7m05s and the axon binary 36.1 MiB → 19.1 MiB.

See it work

echo 'type PatientRecord compliance [HIPAA, GDPR] { ssn: String }
shield PHIShield { scan: [pii_leak] on_breach: halt severity: critical
                   compliance: [HIPAA, GDPR] }
axonendpoint Api { method: POST path: "/p" body: PatientRecord
                   execute: F output: FlowEnvelope<PatientRecord> shield: PHIShield
                   backend: anthropic compliance: [HIPAA, GDPR] }
flow F(ssn: String) -> PatientRecord {
  step R { ask: "summarize" output: PatientRecord } }' > app.axon

axon check   app.axon                  # compile-time compliance verification
axon dossier app.axon                  # regulatory posture, as JSON
axon audit   app.axon --framework all  # per-framework gap analysis

Now delete shield: PHIShield from the endpoint and check again:

X app.axon  1 error(s)
  error [line 4]: axon-T957 axonendpoint 'Api' carries regulated data
  (kappa = {GDPR, HIPAA}) across a trust boundary but declares no `shield:`.
  Regulated boundaries require a shield whose `compliance:` covers the type's
  kappa — the ESK coverage rule. […] Declaring the classes on the
  endpoint's own `compliance:` does NOT cover them: that list is a label,
  the shield is the control that acts on a breach.

axon check exits 1. That is the whole idea: the regulatory property rides on the type system, so it holds at compile time or it does not hold at all.

What's in the box

28 subcommands, all of them listed under every profile. The ones you are most likely to reach for:

axon --help lists all of them.

As a library

[dependencies]
axon-lang = "4"

use axon::*;

Building tooling rather than running programs? The compiler frontend — lexer, parser, AST, epistemic type system, type checker, IR generator — is a separate crate, axon-frontend, with zero runtime dependencies. An LSP, a linter or an analyzer should depend on that and skip the server, database and HTTP stack entirely.

API keys

Only needed to execute flows against real backends — never for axon check, axon compile, axon dossier, axon audit or axon run --tool-mode stub. Seven backends are supported (Anthropic, OpenAI, Gemini, Kimi, GLM, OpenRouter, Ollama); see the repository README for the environment variables each expects.

License

AGPL-3.0-or-later — see LICENSE. Commercial licensing and the enterprise layer are described in the repository.