# tc39-mcp (remote · mcp.xyzzylabs.ai)

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

- Trust score: 63/100 (medium)
- Change this week: +5
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-08-04

## Components

- remote · `mcp.xyzzylabs.ai`: 63/100 (this document), [markdown](https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp.md), [page](https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp)
- npm · `tc39-mcp`: 80/100, [markdown](https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp-2.md), [page](https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp-2)

## Channel facts

- Endpoint: `https://mcp.xyzzylabs.ai/tc39/mcp`
- Transports: `streamable-http`
- Auth: `none`
- Version: `0.6.1`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-08-04.

- **Endpoint Security**: 63/100
  - The endpoint's TLS certificate is valid, in date, and uses a strong key.
  - Authorisation not fully verified: no authorisation is required to call this server, and 17 tool(s) never declared a destructiveHint. The MCP spec treats an absent hint as destructive by default, so we cannot call this surface safe.
  - HTTPS is enforced; there's no plaintext access path.
  - The HSTS (Strict-Transport-Security) header is present.
  - DNSSEC check failed: this domain isn't protected by DNSSEC.
- **Transport & Reachability**: 100/100
  - Verified streamable-http transport via a live MCP handshake.
- **Schema Quality & AI Usability**: 78/100
  - 100% of prompts and resources have a non-trivial description (not blank, and not just the item's name).
  - AI-judged instruction clarity (good).
  - Context-footprint check failed: tool/resource definitions use about 2309 tokens (~135/item across 17 items; 17 tools + 0 resources), over budget; trim descriptions and params.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 30/100
  - Stability observed for 9 of 30 days with no destabilising changes; credit accrues until the full window elapses.
- **Tool Coverage**: 67/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 1% of tool parameters carry a description.
- **Capabilities**: 20/100
  - Spec-recency check failed: implements MCP spec 2024-11-05; the latest is 2026-07-28.

## Install

### Claude

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

### Codex

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

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "xyzzylabs-tc39-mcp": {
      "type": "remote",
      "url": "https://mcp.xyzzylabs.ai/tc39/mcp",
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add xyzzylabs-tc39-mcp --url https://mcp.xyzzylabs.ai/tc39/mcp --transport streamable-http
```

### Hermes

```yaml
mcp_servers:
  xyzzylabs-tc39-mcp:
    url: "https://mcp.xyzzylabs.ai/tc39/mcp"
```

### Other

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

The mcpServers block is a cross-client convention. Remote transports vary, so check your client's docs.

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-08-03 (score 63, +1)

No change was recorded against any check on this day. Stability & Change Management went from 23 to 27. That category is still filling its 30-day observation window: 7 days of observed history at the previous scan, 8 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-08-01 (score 62, +1)

No change was recorded against any check on this day. Stability & Change Management went from 17 to 20. That category is still filling its 30-day observation window: 5 days of observed history at the previous scan, 6 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-31 (score 61, +2)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-30 (score 59, 0)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-29 (score 59, +1)

No change was recorded against any check on this day. Stability & Change Management went from 7 to 10. That category is still filling its 30-day observation window: 2 days of observed history at the previous scan, 3 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-28 (score 58, +1)

No change was recorded against any check on this day. Stability & Change Management went from 3 to 7. That category is still filling its 30-day observation window: 1 days of observed history at the previous scan, 2 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-27 (score 57, 0)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-26 (score 57)

First indexed and scored.

## MCP tools (17)

### `spec.about` (~57 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.

### `clause.get` (~126 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.

Input parameters:

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

### `clause.list` (~98 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.

Input parameters:

- `at` (string)
- `edition` (string)
- `has_algorithm` (boolean)
- `kind` (string)
- `limit` (number)
- `section` (string)
- `spec` (string)

### `spec.search` (~91 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.

Input parameters:

- `at` (string)
- `edition` (string)
- `limit` (number)
- `query` (string, required)
- `search_steps` (boolean)
- `spec` (string)

### `proposal.list` (~105 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).

Input parameters:

- `champion` (string)
- `contains` (string)
- `limit` (number)
- `spec` (string)
- `stage` (string)

### `proposal.get` (~32 tokens)

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

Input parameters:

- `name` (string, required)

### `spec.grammar` (~124 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 productions (off by default).

Input parameters:

- `contains` (string)
- `edition` (string)
- `include_sdo` (boolean)
- `limit` (number)
- `nonterminal` (string)
- `spec` (string)

### `spec.tables` (~86 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.

Input parameters:

- `edition` (string)
- `filter` (string)
- `id` (string)
- `limit` (number)
- `spec` (string)

### `spec.sdo_index` (~107 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).

Input parameters:

- `by` (string)
- `edition` (string)
- `filter` (string)
- `limit` (number)
- `spec` (string)

### `clause.outline` (~84 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.

Input parameters:

- `depth` (number)
- `edition` (string)
- `spec` (string)
- `under` (string)

### `spec.global_search` (~88 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.

Input parameters:

- `limit` (number)
- `query` (string, required)
- `search_steps` (boolean)

### `spec.snapshots` (~96 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.

Input parameters:

- `edition` (string)
- `spec` (string)

### `spec.symbol_resolve` (~91 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.

Input parameters:

- `edition` (string)
- `limit` (number)
- `notation` (string, required)
- `spec` (string)

### `spec.well_known_intrinsics` (~106 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.

Input parameters:

- `edition` (string)
- `filter` (string)
- `limit` (number)
- `spec` (string)

### `spec.diff` (~97 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.

Input parameters:

- `from` (string)
- `id` (string, required)
- `spec` (string)
- `to` (string)

### `spec.crossrefs` (~179 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 `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).

Input parameters:

- `direction` (string)
- `edition` (string)
- `id` (string, required)
- `include_cross_spec` (boolean)
- `limit` (number)
- `spec` (string)

### `test262.search` (~128 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, flags), capped at `limit` (default 20). Supply at least one of `query` / `esid`.

Input parameters:

- `esid` (string)
- `limit` (number)
- `query` (string)

## Diagnostics

Captured diagnostic sections: TLS, DNSSEC, Authorisation, Transports. The full working is on the page: https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp#diagnostics

## Score history

- 2026-08-04: 63
- 2026-08-03: 63
- 2026-08-02: 62
- 2026-08-01: 62
- 2026-07-31: 61
- 2026-07-30: 59
- 2026-07-29: 59
- 2026-07-28: 58
- 2026-07-27: 57
- 2026-07-26: 57

## Links

- Remote endpoint: https://mcp.xyzzylabs.ai/tc39/mcp
- Repository: https://github.com/xyzzylabs/tc39-mcp
- Website: https://mcp.xyzzylabs.ai/tc39
- Changelog RSS feed: https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp/changelog.xml
- Changelog JSON feed: https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp/changelog.json
- HTML version of this page: https://verifymcp.io/servers/xyzzylabs-tc39-mcp/tc39-mcp