axiom

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An agent describes a change set as a Plan. AXIOM compiles it to a canonical, content-addressed Manifest, runs checks over the whole set, and applies it with a hash-gated two-phase commit that leaves a journal and, optionally, a signed attestation. It ships as one npm package — @codai/axiom-mcp — that is an MCP server, a CLI, a PreToolUse hook and a GitHub Action.

Why

• Per change set, not per tool call. Harness hooks (Claude Code, Copilot, Cursor) decide one write at a time. A forty-file refactor is forty blind decisions; AXIOM checks the whole manifest first — "if you touch X you must also touch Y", dependency budgets, secrets, paths.

• Byte-exact. The manifest is JCS-canonical (RFC 8785) and holds only sha256 digests; apply demands the digest you inspected (confirmDigest), re-hashes every pre-image at commit, and rolls back to the byte-identical prior tree on any failure — on a tree several agents share.

• Provable. Every apply leaves a journal keyed by digest. Manifests can be DSSE-signed with pinned Ed25519 keys and anti-rollback counters; verify --tree proves a tree matches a manifest and emits an in-toto attestation that CI uploads to Sigstore.

Related MCP server: contextos-memory

What it does

flowchart LR
  subgraph entry [Entry points]
    direction TB
    MCP[MCP server<br/>stdio · Streamable HTTP]
    CLI[CLI<br/>axiom compile · check · apply]
    HOOK[PreToolUse hook<br/>axiom gate --stdin]
    GHA[GitHub Action<br/>dragoscv/axiom/action@v2]
  end
  P[Plan<br/>JSON or .axm] -->|compile| M[Manifest<br/>JCS · sha256 per file<br/>blobs · CAS · ref · patch]
  M -->|check| C[CheckReport<br/>pass · fail · error]
  C -->|apply · 2PC<br/>confirmDigest| T[Repository tree]
  T --> J[Journal · ApplyResult<br/>DSSE signature · in-toto attestation]
  J -.->|rollback| T
  entry --> P

Install

Binaries ship with SHA256SUMS and Sigstore provenance; npm packages carry npm provenance. How to check them: SECURITY.md.

Quickstart (60 s)

1. Point an MCP client at a repo — .vscode/mcp.json (Claude Desktop config is the same shape, see packages/mcp/README.md):

{
  "servers": {
    "axiom": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@codai/axiom-mcp", "mcp", "--root", "${workspaceFolder}"]
    }
  }
}

--root is an explicit allowlist and may repeat; there is no cwd or env fallback.

2. Write a Plan — plan.json:

{
  "apiVersion": "axiom.dev/v2",
  "kind": "Plan",
  "name": "hello",
  "intent": "Add a greeting module and document it.",
  "artifacts": [
    { "path": "src/hello.ts",
      "source": { "type": "inline", "content": "export const hi = () => 'hi';\n" } },
    { "path": "README.md", "op": "overwrite",
      "source": { "type": "inline", "content": "# hello\n" } }
  ],
  "checks": [{ "id": "no-secrets", "predicate": "content.noSecrets", "params": {} }]
}

3. Compile → check → apply from the CLI (the MCP tools do the same):

axiom compile plan.json --root . -o bundle.json        # → { manifestDigest: "sha256:…" }
axiom check   bundle.json --root .                     # → CheckReport, verdict pass|fail|error
axiom apply   bundle.json --root . --dry-run           # unified diff, nothing written
axiom apply   bundle.json --root . --confirm sha256:…  # two-phase commit, journal under .axiom/
axiom rollback sha256:… --root .                       # reverse-replay that journal entry

Plan fields, sources (inline, cas, ref, patch, template) and the .axm DSL: docs/reference/plan-format.md · docs/reference/axm-syntax.md.

Use it as a PreToolUse hook

axiom gate --stdin reads one harness payload, checks containment, path.deny/allow, content.noSecrets and content.maxBytes on the write target, scans shell commands for write primitives, and answers allow (exit 0) or deny (exit 2, JSON reason). Fail-closed; ~100 ms end to end. Claude Code:

{ "hooks": { "PreToolUse": [ { "matcher": "Write|Edit|MultiEdit|NotebookEdit",
  "hooks": [ { "type": "command", "command": "axiom gate --stdin", "timeout": 5 } ] } ] } }

Copilot CLI / VS Code wiring, profile file and the latency budget: docs/getting-started/hooks.md.

Use it in CI

Fail a pull request whose tree does not match the manifest an agent applied, and optionally upload an in-toto attestation:

- uses: dragoscv/axiom/action@v2
  with:
    bundle: .axiom/manifests/<hex>.json
    root: .
    attest: true   # needs permissions: id-token: write, attestations: write

Scope, --pre mode and how to verify the attestation later: docs/guides/verify-tree.md.

Tools

Seventeen MCP tools, each with annotations and an outputSchema; errors are isError results carrying a code from the closed ERROR_CODES enum — a handler never throws.

Inputs, outputs, resources (axiom://…), transports (--wire 2026|2025) and the error contract: docs/reference/mcp-tools.md. CLI verbs (sign, trust, gc, migrate v1, snapshot, …): packages/mcp/README.md.

Architecture

flowchart TB
  schema["@codai/axiom-schema<br/>Zod v4 · ERROR_CODES · JSON Schema"]
  canon["@codai/axiom-canon<br/>JCS · sha256 · in-toto · DSSE"]
  plan["@codai/axiom-plan<br/>compile · CAS · ref · patch"]
  checks["@codai/axiom-checks<br/>18 predicates · profiles · guards"]
  apply["@codai/axiom-apply<br/>containment · 2PC · journal · verify-tree"]
  axm["@codai/axiom-axm<br/>.axm parser"]
  lsp["@codai/axiom-axm-lsp<br/>language server"]
  web["@codai/axiom-emitters-web<br/>template emitter"]
  mcp["@codai/axiom-mcp<br/>MCP server · CLI · gate"]
  plan --> schema & canon
  checks --> schema & canon
  apply --> schema & canon
  axm --> schema
  lsp --> axm & schema
  mcp --> plan & checks & apply & axm & web & canon & schema

schema and canon are leaves; plan, checks, apply depend only on those two; axm on schema; axm-lsp on axm + schema; emitters-web has no workspace deps (the emitter registry is an interface injected into compilePlan); mcp depends on everything except the private testkit; nobody depends on mcp. Enforced by check-package-deps.

Invariants (never weakened; PLAN.md §2, design):

1. ManifestBody is JCS-canonical; manifestDigest = sha256(JCS(body)); nothing hashed contains a timestamp.

2. Content never lives in the manifest — it travels as blobs (≤ 256 KiB each, ≤ 4 MiB bundle), CAS (.axiom/cas/sha256/…) or a digest-pinned ref.

3. apply requires confirmDigest === manifestDigest; pre-images are re-verified at commit; .axiom/lock = single writer per root.

4. Error codes are a closed enum; tests and clients branch on code, never on message text.

5. MCP stdout is JSON-RPC only; logs to stderr at warn.

6. No shell: child processes get an args array, never shell: true.

7. A predicate whose fact provider cannot run yields verdict: "error" — fail closed.

8. Roots are an explicit allowlist (--root); no cwd fallback.

9. The MCP SDK is reached through one seam (packages/mcp/src/adapter.ts) and lives in lazy chunks.

Packages

Private, not published: testkit (golden fixtures, arbitraries), conformance (MCP conformance harness), vscode-axm (the .vsix). All nine public packages share one version (fixed Changesets group) and are released together.

Checks & profiles

A Profile is a list of typed predicates. Built-ins: path.allow / path.deny / path.reservedNames, content.noSecrets / content.maxBytes / content.encodingUtf8, manifest.maxArtifacts / manifest.maxTotalBytes / manifest.requireSigned / manifest.noDeletes, deps.max / deps.deny, repo.noOverwriteOf / repo.requireCompanion, guard.external (your own scripts/check-*.mjs), expr.cel and expr.cedar (offline policy languages). Verdict is pass | fail | error; anything that cannot be evaluated is error, which blocks apply. Catalogue, params and profile authoring: docs/guides/checks.md.

Signing & provenance

axiom keygen → axiom trust add → axiom sign puts a detached DSSE envelope (Ed25519 over JCS(manifest)) beside the bundle without changing its digest; a profile with manifest.requireSigned then refuses unsigned, tampered, untrusted or replayed (antiRollback) bundles. axiom verify --tree [--attest] emits an in-toto Statement (https://axiom.dev/attestation/apply/v1). Envelope, key ceremony, root binding and limits: docs/guides/signing.md · docs/guides/verify-tree.md.

Status & roadmap

2.3.x shipped. Plan compiler with every source type, 18 predicates, fail-closed apply with journal/rollback/PR mode, MCP SDK v2 (2026-07-28 wire, --wire 2025 fallback) over stdio and HTTP with 17 tools, fail-closed gate, .axm DSL + LSP + VS Code extension, DSSE signing, verify --tree + attestation + GitHub Action, CI on ubuntu/windows/macos, 18 repo guards. 2.2.1 adds standalone binaries with provenance, the MCP Registry listing, the docs site and the action@v2 tag. codai's SWE harness routes every write through the gate by default (docs/integration/codai.md); brivio and metu wirings are in docs/integration/.

Decisions (D-xx) and stories (S-xxx): PLAN.md · TRACKER.csv · MIGRATION.md for 1.x users · docs/reference/versioning.md.

Development

pnpm 12 · Node ≥ 22.14 · TypeScript 7 (tsgo) · tsdown · Biome · Vitest 5 · fast-check · Changesets.

pnpm install --frozen-lockfile
pnpm lint          # biome check .
pnpm build         # tsdown every package (before typecheck — exports point at dist/)
pnpm typecheck
pnpm test          # vitest run
pnpm guards        # node scripts/run-guards.mjs — 18 repo invariants

All five green with output shown, a .changeset/*.md for anything under packages/*/src, and the ripple closed (tool → docs/reference/mcp-tools.md + packages/mcp/README.md + spec/tools.json; schema → regenerated schemas/*.json; golden → re-pinned). Details: CONTRIBUTING.md and .github/instructions/.

Community

Discussions for questions · Issues for bugs and features · SUPPORT.md · SECURITY.md (private reporting) · CODE_OF_CONDUCT.md · CITATION.cff.

License

MIT © Dragos Catalin Vladulescu.