tc39-mcp

Measured conclusion: Deep-tested. L2 outcome: tools_ok.

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

Add to your agent

Copy this into your MCP client config:

{
  "mcpServers": {
    "tc39-mcp": {
      "url": "https://mcp.xyzzylabs.ai/tc39/mcp",
      "transport": "streamable-http"
    }
  }
}

Measured tools (17)

• 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, edition), plus test262 + proposals index headers when present.

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 snapshot (only valid for edition='main'); omit to query the live snapshot.

  Parameters:

  • id (required) — string
  • at — string — Optional historical SHA pin (hex, 4-40 chars). Only valid when edition='main'; released editions have no per-SHA history to address.
  • spec — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 snapshot.

  Parameters:

  • at — string
  • kind — string
  • spec — string
  • limit — number
  • edition — string
  • section — string
  • has_algorithm — boolean

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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.

  Parameters:

  • query (required) — string
  • at — string
  • spec — string
  • limit — number
  • edition — string
  • search_steps — boolean

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 (substring), or contains (name/slug substring).

  Parameters:

  • spec — string
  • limit — number
  • stage — string
  • champion — string
  • contains — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• proposal.get

  Fetch one TC39 proposal by slug (exact) or name (case-insensitive).

  Parameters:

  • name (required) — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• spec.grammar

  Query grammar productions captured from the spec's `<emu-grammar>` blocks. `{ nonterminal }` returns every production for that non-terminal (exact match); `{ contains }` filters by RHS / name substring; neither lists all non-terminals + their production counts. `include_sdo` folds in SDO-attached productions (off by default).

  Parameters:

  • spec — string
  • limit — number
  • edition — string
  • contains — string
  • include_sdo — boolean
  • nonterminal — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 `filter` substring over the caption or id.

  Parameters:

  • id — string
  • spec — string
  • limit — number
  • filter — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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'` groups productions under each SDO title. `filter` narrows to keys containing a substring (case-insensitive).

  Parameters:

  • by — string
  • spec — string
  • limit — number
  • filter — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 to descendants of one clause id.

  Parameters:

  • spec — string
  • depth — number
  • under — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 know which spec defines a symbol. `search_steps` also matches algorithm step text.

  Parameters:

  • query (required) — string
  • limit — number
  • search_steps — boolean

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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'). Historical SHA-pinned copies are reachable via `at:` on clause.get / spec.search but aren't enumerated here.

  Parameters:

  • spec — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• spec.symbol_resolve

  Resolve spec notation like `[[Prototype]]` (internal slot), `%Object.prototype%` (well-known intrinsic), or `~number~` (sigil enum): return clauses that mention or define it, ranked by occurrence with a bump for definition-y sections.

  Parameters:

  • notation (required) — string
  • spec — string
  • limit — number
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 `%X%` prose scan (e.g. ECMA-402). `filter` narrows by bare-name substring.

  Parameters:

  • spec — string
  • limit — number
  • filter — string
  • edition — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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, step count, reworded step indices, notes, crossrefs). `from` defaults to the latest stable release, `to` to main.

  Parameters:

  • id (required) — string
  • to — string
  • from — string
  • spec — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 doesn't expose). The reverse index is AOID-densified from step text. `direction`: 'in' | 'out' | 'both' (default). Outgoing also carries an `external` category: the clause's citations to external specs (Unicode, IETF, WHATWG) as resolvable URLs. Set `include_cross_spec: true` to also resolve outgoing references from ECMA-262 → ECMA-402 (or vice versa).

  Parameters:

  • id (required) — string
  • spec — string
  • limit — number
  • edition — string
  • direction — string
  • include_cross_spec — boolean

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

• 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 + path; `esid` prefix-matches the front-matter esid. Returns ranked hits (path, GitHub url at the indexed SHA, esid, description, features, flags), capped at `limit` (default 20). Supply at least one of `query` / `esid`.

  Parameters:

  • esid — string
  • limit — number
  • query — string

  Hints: read-only not declared · destructive not declared · idempotent not declared · open-world not declared

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