wasm-mcp

Model Context Protocol server for the
WebAssembly core specification.
SHA-pinned, read-only, deterministic — safe to host as a public
unauthenticated endpoint.

Not affiliated with, endorsed by, or sponsored by the W3C
WebAssembly Community Group or Working Group.

What it gives you

• spec_version — the pinned upstream commit and package version.
• instruction_get — opcode bytes, category, introducing version,
  stack type signature, validation + execution prose anchors / URLs,
  and trap conditions (traps + can_trap), by mnemonic (i32.add)
  or binary opcode (0x6a).
• instruction_list — enumerate, filterable by category (numeric,
  vector, reference, parametric, variable, table, memory, control,
  ref, i31, struct, array, extern), introducing version, or prefix.
• instruction_search — ranked free-text search across mnemonics,
  categories, and opcodes.
• type_get — value types (number / vector / reference) and type
  forms (functype, limits, memtype, …) with defining prose.
• section_get — one spec clause by id / anchor (structure,
  validation, execution, binary, text), with prose, cross-references,
  SpecTec formal-rule references, and the rendered URL.
• section_list — navigate the clause tree by area or anchor prefix.
• spec_search — full-text search across anchors, titles, and prose.
• proposal_list — WebAssembly proposals and their phases (from the
  pinned WebAssembly/proposals repo), filterable by status, phase,
  champion, or affected spec.

section_get, section_list, and spec_search take a spec
argument covering all three specs in the WebAssembly/spec repo:
core (default), js-api (the JavaScript embedding API), and
web-api (Web-platform integration). The instruction and type tools
are core-only.

Contract

Every tool is:

• Read-only. No state mutation, no writes outside an optional
  local cache.
• Deterministic. Same input → same output, over the pinned spec
  commit recorded in vendor/PINNED.txt.
• No execution. Never compiles, validates-by-running,
  instantiates, or runs any WebAssembly or arbitrary code. Validation
  and reduction rules are returned as data.
• No auth, no secrets, no PII. Usable anonymously.
• No network at request time. All spec data is fetched and
  indexed at build time and baked into the package.

Install (stdio, local)

npx wasm-mcp

Wire into Claude Code by adding to your project's .mcp.json:

{
  "mcpServers": {
    "wasm": {
      "type": "stdio",
      "command": "npx",
      "args": ["wasm-mcp"]
    }
  }
}

Hosted Worker

The Cloudflare Worker in worker/ exposes the same tool
surface as the stdio package over streamable HTTP at a single
unauthenticated endpoint, rate-limited per source IP (30 req / 60 s):

https://wasm-mcp.chicoxyzzy.workers.dev/mcp

GET /health reports status and the pinned SHAs; GET /privacy
states the anonymous, no-storage posture. All spec data is bundled
into the Worker, so it does pure in-memory lookups — no storage, no
network at request time.

Releases & data refresh

The pinned commits live in vendor/PINNED.txt
and are reported by spec_version. A scheduled GitHub Actions
workflow (refresh.yml) SHA-diffs
the upstream repos daily; when a pin moves it re-pins, bumps the patch
version, and tags a release, which publishes the npm package
(release.yml) and redeploys the
Worker (deploy-worker.yml).

Maintainers:

• npm publish uses Trusted Publishing
  (OIDC) — no NPM_TOKEN. Configure it once on npmjs.com (wasm-mcp →
  Settings → Trusted Publisher → GitHub Actions: org xyzzylabs, repo
  wasm-mcp, workflow release.yml).
• Worker deploy needs CLOUDFLARE_API_TOKEN + CLOUDFLARE_ACCOUNT_ID,
  stored as environment secrets on the cloudflare GitHub
  Environment (not repo-wide) with a main + v* deployment rule —
  see Securing the deploy credentials.
• For the refresh workflow's tag push to trigger release + deploy,
  add a WORKFLOW_PAT PAT (contents: write + workflows) —
  without it, refresh still re-pins and tags, but you run release /
  deploy manually. (Same secret name tc39-mcp uses, so one PAT — or an
  xyzzylabs org secret — can serve both repos.)

License

MIT — see LICENSE.