io.github.xyzzylabs/tc39-mcp

up checked 2026-11-11T06:38:00.300Z

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Publisher-provided title

tc39-mcp

Publisher-provided description

Independent MCP server for the TC39 specs (ECMA-262 + ECMA-402): clauses, search, diffs, history.

Summary by lookupd

Lets agents fetch, search, diff and cross-reference TC39 ECMAScript spec clauses, proposals and test262 conformance tests.

Install

Claude Code, remote (streamable-http)

claude mcp add --transport http tc39 https://mcp.xyzzylabs.ai/tc39/mcp

Claude Code, npm package (stdio)

claude mcp add tc39 -- npx -y tc39-mcp

Codex, remote (streamable-http)

codex mcp add tc39 --url https://mcp.xyzzylabs.ai/tc39/mcp

Codex, npm package (stdio)

codex mcp add tc39 -- npx -y tc39-mcp

Cursor, remote (streamable-http) → .cursor/mcp.json

{
  "mcpServers": {
    "tc39": {
      "url": "https://mcp.xyzzylabs.ai/tc39/mcp"
    }
  }
}

Cursor, npm package (stdio) → .cursor/mcp.json

{
  "mcpServers": {
    "tc39": {
      "command": "npx",
      "args": [
        "-y",
        "tc39-mcp"
      ]
    }
  }
}

Other clients: docs. Or tell your agent: Set up lookupd for me: read https://lookupd.com/agent.md and follow it.

Tools (17 tools)

Publisher-provided text

• spec.about Self-description of this MCP server: package name + version, per-snapshot pin metadata (sha, fetched_at, biblio_commit, clause_count) for every supported (spec,
• clause.get Fetch a parsed TC39 clause as structured JSON. `spec` selects '262' (default) or '402'. `edition` defaults to 'latest'. `at: '<sha>'` pins to a historical main
• clause.list List parsed spec clauses with optional filters (kind, section prefix, has_algorithm). `spec` selects '262' or '402'. `at: '<sha>'` queries a historical main sna
• spec.search Search the parsed spec by clause id / aoid / title (+ step text with `search_steps`). Aoid-exact ranks first. `at: '<sha>'` searches a historical main snapshot.
• proposal.list List TC39 proposals from the static index (tc39/proposals). Filter by spec ('262'|'402'), stage ('0'|'1'|'2'|'2.7'|'3'|'finished'|'inactive'|'active'), champion
• proposal.get Fetch one TC39 proposal by slug (exact) or name (case-insensitive).
• spec.grammar Query grammar productions captured from the spec's `<emu-grammar>` blocks. `{ nonterminal }` returns every production for that non-terminal (exact match); `{ co
• spec.tables List or fetch parsed `<emu-table>` content. `{ id }` returns exactly that table (full columns + rows); otherwise list table summaries, optionally narrowed by a
• spec.sdo_index Index Syntax-Directed Operations by the grammar production they're defined on. `by: 'production'` (default) groups SDOs under each production; `by: 'sdo'` group
• clause.outline Return the section tree (table of contents) for a parsed (spec, edition). `depth` caps how deep the tree descends (1 = top-level only); `under` limits the tree
• spec.global_search Run spec.search across both ECMA-262 and ECMA-402 in one call and interleave hits by score. Each hit is tagged with the spec it came from. Use it when you don't
• spec.snapshots List the live (spec, edition, sha, fetched_at) snapshots the hosted Worker is serving from R2. Filter by `spec` ('262'|'402') or `edition` (e.g. 'main', 'es2026
• spec.symbol_resolve Resolve spec notation like `[[Prototype]]` (internal slot), `%Object.prototype%` (well-known intrinsic), or `~number~` (sigil enum): return clauses that mention
• spec.well_known_intrinsics Enumerate the well-known intrinsics in a spec with their probable defining clauses. Driven from the canonical §6.1.7.4 WKI table when present (ECMA-262), else a
• spec.diff Clause-level diff of one clause across two editions of a spec. Reports identical / modified / added / removed plus a field-level breakdown (title, signature, st
• spec.crossrefs For a clause id, return its outgoing references (clauses it cites) and/or incoming references (clauses that cite it — the back-reference index the parse alone d
• test262.search Search the tc39/test262 conformance suite from its indexed front-matter. `query` AND-matches whitespace tokens (case-insensitive) across each test's description

Details

• Version: 0.6.6
• Transports: streamable-http, stdio
• Uptime (7 days): 100%
• Median latency: 253 ms
• First indexed: 2026-11-01T10:01:02.123Z
• Last seen in registry: 2026-11-07T20:17:14.129Z
• Repository: https://github.com/xyzzylabs/tc39-mcp
• Website: https://mcp.xyzzylabs.ai/tc39

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