mcp server
tc39-mcp
Independent MCP server for the TC39 specs (ECMA-262 + ECMA-402): clauses, search, diffs, history.
Description as published by the maintainer. Source
- version 0.6.1
- active
- retrieval
active — Registry entry last updated 2026-07-07. Dashed tags are derived by ZBS Index from the published description, not stated by the maintainer.
What this server can do
17 functions, named and described by the server itself. Parameter names are shown because they say more about what a function does than its name usually does.
clause.get(at, id, spec, edition)- 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. Required: id.
clause.list(at, kind, spec, limit, edition, section, has_algorithm)- 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(spec, depth, under, edition)- 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(name)- Fetch one TC39 proposal by slug (exact) or name (case-insensitive). Required: name.
proposal.list(spec, limit, stage, champion, contains)- 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- 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(id, spec, limit, edition, direction, include_cross_spec)- 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). Required: id.
spec.diff(id, to, from, spec)- 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. Required: id.
spec.global_search(limit, query, search_steps)- 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. Required: query.
spec.grammar(spec, limit, edition, contains, include_sdo, nonterminal)- 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).
spec.sdo_index(by, spec, limit, filter, edition)- 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(at, spec, limit, query, edition, search_steps)- 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. Required: query.
spec.snapshots(spec, edition)- 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(spec, limit, edition, notation)- 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. Required: notation.
spec.tables(id, spec, limit, filter, edition)- 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(spec, limit, filter, edition)- 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(esid, limit, query)- 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`.
Last successful function declaration observed on . Source: https://mcp.xyzzylabs.ai/tc39/mcp. We list what the server declared; we do not call any of these functions.
Endpoint status observed on . Source: https://mcp.xyzzylabs.ai/tc39/mcp.
Signals
These are separate measurements of different things. They are deliberately not combined into one score, because a popularity number that mixes website traffic with saves and stars cannot be checked or acted on.
| Signal | Value | What it measures | Window | Observed | Source |
|---|---|---|---|---|---|
| Latest published version | 0.6.1 | Latest version string the maintainer published to the registry. | as of fetch | Model Context Protocol | |
| Registry record last updated | 2026-07-07 | When the registry record was last updated by its maintainer. | point in time | Model Context Protocol | |
| First listed in the MCP Registry | 2026-07-07 | Date this server was first published to the official MCP Registry. Not a usage or quality measure. | point in time | Model Context Protocol | |
| mcp tools declared | 17 tools | Number of functions the server itself declared when asked to list them. This is what the server offers an agent, not a measure of how well any of them work. | as of probe | mcp.xyzzylabs.ai | |
| mcp endpoint status | ok | The server listed 17 functions when asked. | as of probe | mcp.xyzzylabs.ai |
Where to get it
Also from xyzzylabs
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wasm-mcp
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This record as data
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