MCP server

tc39-mcp

io.github.xyzzylabs/tc39-mcp

Checked 26 Oct 2026, 08:29 UTC · Connected to it and listed its tools

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

Website Source

At a glance

Type

MCP server

Publisher

xyzzylabs.ai (verified by the MCP Registry)

Status

Working at last check

Tools

17

Token cost

About 2,352 tokens per request

Sets up in

Claude Code, Claude Desktop, Codex, Gemini CLI, Cursor, VS Code, Antigravity, ChatGPT, OpenAI API, Grok

Last checked

26 Oct 2026, 08:29 UTC

Connect it to your agent

Add to CursorAdd to VS CodeVS Code Insiders

Opens the app, which shows the server and asks you to confirm. For other apps, copy the setup below.

Claude Code

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

Claude Desktop

Settings → Connectors → Add custom connector, and paste the URL.

Codex (config.toml)

[mcp_servers.tc39-mcp]
url = "https://mcp.xyzzylabs.ai/tc39/mcp"

Gemini CLI

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

Cursor

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

VS Code

{"servers":{"tc39-mcp":{"type":"http","url":"https://mcp.xyzzylabs.ai/tc39/mcp"}}}

Antigravity

agy mcp add tc39-mcp https://mcp.xyzzylabs.ai/tc39/mcp

ChatGPT

Settings → Apps & Connectors → Advanced settings: turn on Developer mode, then Create a connector and paste the URL. Which plans can do this varies.

OpenAI API (Responses tools)

{"type":"mcp","server_label":"tc39-mcp","server_url":"https://mcp.xyzzylabs.ai/tc39/mcp","require_approval":"always"}

Grok (xAI API tools)

{"type":"mcp","server_label":"tc39-mcp","server_url":"https://mcp.xyzzylabs.ai/tc39/mcp"}

Tools

• clause.get ~174 tokens
  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.
• clause.list ~133 tokens
  List parsed spec clauses with optional filters (kind, section prefix, has_algorithm). `spec` selects '262' or '402'. `at: '<sha>'` queries a historical main snapshot.
• clause.outline ~117 tokens
  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.
• proposal.get ~58 tokens
  Fetch one TC39 proposal by slug (exact) or name (case-insensitive).
• proposal.list ~130 tokens
  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).
• spec.about ~97 tokens
  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.
• spec.crossrefs ~241 tokens
  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 `
• spec.diff ~141 tokens
  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.
• spec.global_search ~127 tokens
  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.
• spec.grammar ~174 tokens
  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 pr
• spec.sdo_index ~152 tokens
  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).
• spec.search ~129 tokens
  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.
• spec.snapshots ~125 tokens
  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.
• spec.symbol_resolve ~138 tokens
  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.
• spec.tables ~126 tokens
  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.
• spec.well_known_intrinsics ~133 tokens
  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.
• test262.search ~157 tokens
  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,

Browse

• GitHub tools
• GitHub and code hosting

Related MCP servers

• SpecProof
  SpecProof: Search standards specs with MCP-ready precision.
• wasm-mcp
  Read-only MCP server for the WebAssembly spec: instructions, types, sections, search, proposals.
• 19hz
  19hz.info MCP.
• Autopia
  Verified, reproduced behavior of public HTTP APIs: spec gaps, errors, pagination, auth.
• Whirrwork
  Robot jobs, sourced prices with history, providers by country, robot-vs-human costs, and RFQs.
• Legislation
  U.S. bills, roll-call votes, legislators and 2026 elections for all 50 states, D.C. and Congress.
• Api Diff Monitor
  Cloudflare Workers MCP server: api-diff-monitor
• oasdiff
  Detect breaking changes, generate changelogs, diff, and validate OpenAPI specs.

Badge for your README

[![AptLynx](https://aptlynx.net/badge/io.github.xyzzylabs/tc39-mcp.svg)](https://aptlynx.net/servers/io.github.xyzzylabs/tc39-mcp)

Listing text is written by the maker; AptLynx lists tools and does not vouch for them. Find another tool · Browse by topic · For agents