Lexapi MCP README

LexAPI MCP

Model Context Protocol server for LexAPI — EU law for AI assistants: EUR-Lex legislation parsed to article level, CJEU case law, the typed citation graph, and semantic search (including the law as in force on a past date). Works with Claude, Cursor, VS Code and any other MCP client.

Ask your assistant "what does Article 17 GDPR require?", "which acts amended REACH?" or "what were the own-funds requirements for banks in June 2019?" — the model calls LexAPI and answers from the source text, with CELEX citations.

You need a LexAPI API key. Create one for free at lex-api.com/dashboard — the FREE plan includes 500 credits a month, no card required, enough to try the read tools.

Install

Claude Desktop

Add to claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "lexapi": {
      "command": "npx",
      "args": ["-y", "@lexapi/mcp"],
      "env": { "LEXAPI_API_KEY": "lex_..." }
    }
  }
}

Restart Claude Desktop.

Claude Code

claude mcp add lexapi --env LEXAPI_API_KEY=lex_... -- npx -y @lexapi/mcp

Cursor, VS Code and other stdio clients

Run npx -y @lexapi/mcp with LEXAPI_API_KEY in the environment (Cursor: ~/.cursor/mcp.json; VS Code: .vscode/mcp.json; same command / args / env shape as above).

Hosted server (no local install)

The same tools are served over Streamable HTTP at https://mcp.lex-api.com/v1, authenticated with your key as Authorization: Bearer lex_... (or x-api-key: lex_...):

claude mcp add --transport http lexapi https://mcp.lex-api.com/v1 --header "Authorization: Bearer lex_..."

The npm package needs Node.js 20 or newer.

Tools

Every call is billed from your LexAPI credit pool exactly like the REST endpoint it wraps; each tool's description states its cost so the model can see it.

How results are shaped for models

• Compact output. Responses drop envelopes and duplicate legacy fields. Documents keep their metadata, textAvailability (why text is missing, which languages exist, a pointer to the latest consolidated version) and language-fallback labels.
• Large documents. lex_get_document returns the whole body when it fits maxChars (default 40,000 characters), otherwise an outline (article ids, section tree, counts). Fetch an article with articleId or parts with include; long parts continue with offset.
• Consolidated texts are not authentic. Consolidated versions carry consolidated: true, consolidatedAsOf, baseCelex and a note: quote them, cite the act as published in the Official Journal.
• asOf. Each legislation hit says whether it carries the version in force on that date (asOfResolved, asOfVersion); unresolved hits keep the current text with an asOfReason, and the response warns about them.
• Errors say what to do. A 402 states the credits needed, the credits left and the reset date; a 429 says how long to wait.

Configuration

The key is sent only as the x-api-key header to LexAPI; it is never logged or included in tool output. A key containing whitespace or control characters (e.g. a multi-line paste) is rejected at startup.

Timeouts. MCP clients give up on a tool call after their own timeout (60 s by default in the official SDK; Claude Code: MCP_TOOL_TIMEOUT). A first, live EUR-Lex fetch can take longer. The server gives each tool call one 55 s deadline — retries and rate-limit waits included — and then returns a message the model can act on, instead of the client's generic timeout error. When the client sends a progress token, the server also sends a progress notification every 10 s; whether that keeps the call alive is up to the client (the official SDK only extends its timeout on progress when the caller opts into resetTimeoutOnProgress, and a server cannot detect that), so the deadline stays 55 s. If you raise your client's timeout, raise LEXAPI_TIMEOUT_MS to match. Cancelling a call aborts the request to LexAPI.

Troubleshooting

• LEXAPI_API_KEY is not set — the variable isn't reaching the spawned process; check the env block of your MCP client config.
• LexAPI error 401 — the key is wrong or revoked; create a new one at the dashboard.
• LexAPI error 402 (CREDITS_EXHAUSTED) — the monthly credit pool is used up. The message gives the reset date; top-ups and upgrades are on the dashboard.
• LexAPI error 429 — the per-minute rate limit of your key (FREE: 15 per minute). Short waits are retried once automatically; otherwise the message says how long to wait.
• LexAPI error 403 — the plan doesn't include the feature (e.g. export below BUSINESS, or semantic search on a legacy pre-credits FREE plan).
• LexAPI error 400 creating a webhook — the details name the problem (unsupported criteria, a watch list over the plan limit, or the plan's webhook limit; FREE has none).

Development

git clone https://github.com/Lex-API/lexapi-mcp.git
cd lexapi-mcp
npm install
npm test                       # build + unit and transport tests (mocked API, no network)
npm run typecheck && npm run lint
node scripts/smoke-stdio.mjs   # stdio smoke test against a local mock API
LEXAPI_API_KEY=lex_... node scripts/smoke-stdio.mjs --live   # against the real API (spends roughly 6–25 credits)

npm run start:http runs the hosted Streamable HTTP transport (POST /v1, GET /health, port from PORT, default 3000); the Dockerfile builds it.

License

MIT