Tc39 MCP

📖 Docs: mcp.xyzzylabs.ai/tc39 - Get started · Tools · Cookbook · Editions · Architecture · Hosting

People who work with ecma262, ecma402 and ecmascript and want it reachable from Claude, Cursor, VS Code, or another MCP client. The project is written in TypeScript.

VERIFIED ACTIVE

LAST COMMIT 2026-09-17 · ★ 2 · #296 OF 945 MAINTAINED OTHER · VERIFIED 2026-09-18

MIT · TypeScript servers · how we verify → /methodology

01 · Install Tc39 MCP

before you install - you'll need

Set TC39_MCP_BASE_URL before connecting.

Claude Code

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

Claude Desktop / Cursor / VS Code - add to config

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

Same JSON for Cursor. For VS Code, rename the top-level key from `mcpServers` to `servers`.

Using another client? Same JSON, different key

Claude Desktop · mcpServers

Cursor · mcpServers

VS Code · servers

Windsurf · mcpServers

Zed · context_servers

Cline · mcpServers

Roo Code · mcpServers

Continue · mcpServers

LibreChat · mcpServers

Gemini CLI · mcpServers

Codex CLI · mcp_servers

Full setup guides: every client.

02 · Evidence

https://mcp.xyzzylabs.ai/tc39/mcp

transport: streamable-http

endpoint alive - responded to MCP initialize · probed 2026-09-18

Security posture

What to check before giving this server access to your agent - from the registry, GitHub, and our own probes. We don't score safety; we show what's verifiable.

runs as local process (stdio) - runs on your machine with your user's permissions · remote - your agent's requests go to mcp.xyzzylabs.ai

endpoint auth accepted our unauthenticated MCP initialize - no credentials needed to connect

license MIT - declared in the repository

npm package tc39-mcp - unscoped; check the name against the project README before installing

registry namespace io.github.xyzzylabs is GitHub-verified and matches the repo owner

03 · What Tc39 MCP can do

Prose above is summarized from the project's README and registry record - no invented capabilities.

Latest releases

v0.6.3 · 2026-09-08

Automated PATCH refresh - upstream tc39/ moved. Same code, new spec data. See spec.about for the current SHAs.

v0.6.2 · 2026-08-07

Automated PATCH refresh - upstream tc39/ moved. Same code, new spec data. See spec.about for the current SHAs.

v0.6.1 · 2026-07-07

Automated PATCH refresh - upstream tc39/ moved. Same code, new spec data. See spec.about for the current SHAs.

04 · Who maintains Tc39 MCP

tc39-mcp is maintained by xyzzylabs. We track 2 MCP servers from xyzzylabs - 2 actively maintained, 4 combined GitHub stars, oldest repo from May 2026. Full record: all servers from xyzzylabs.

  1. wasm-mcp Read-only MCP server for the WebAssembly spec: instructions, types, sections, search, proposals. ★ 2

05 · Facts

repository
github.com/xyzzylabs/tc39-mcp
website
https://mcp.xyzzylabs.ai/tc39
category
other - ranked #296 of 945 actively-maintained other servers as of 2026-09-18.
release cadence
6 releases in the last 90 days (latest 2026-09-08)
registry
io.github.xyzzylabs/tc39-mcp (active, first published 2026-05-31 · 17 versions)
packages
npm:tc39-mcp

06 · Tc39 MCP FAQ

What is Tc39 MCP?

📖 Docs: mcp.xyzzylabs.ai/tc39 - Get started · Tools · Cookbook · Editions · Architecture · Hosting

Is Tc39 MCP still maintained?

Yes - as of 2026-09-18, its last commit was 2026-09-17 and it shipped 6 releases in the last 90 days. We re-verify nightly.

How do I install Tc39 MCP?

Run `npx -y tc39-mcp`. The README documents one environment variable (TC39_MCP_BASE_URL) to set first. Set TC39_MCP_BASE_URL before connecting. You can also paste the ready-made client config above.

Does Tc39 MCP require authentication?

No - the endpoint accepted our unauthenticated MCP initialize when probed on 2026-09-18; you can connect without credentials.

07 · Alternatives to Tc39 MCP

Alternatives to Tc39 MCP

Maintained other servers if Tc39 MCP isn't the fit.

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  6. Microsoft Fabric MCP Server MCP tools for interacting with Microsoft Fabric ★ 3,681 · 2026-09-17

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