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.

Related MCP server: speclib-mcp

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 it into any MCP client by adding the server to its config (the launch command is the same everywhere; only the config file differs):

{
  "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://mcp.xyzzylabs.ai/wasm/mcp

GET /wasm/health reports status and the pinned SHAs; GET /wasm/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.