Cursor

Cursor connects to remote Streamable HTTP servers from a mcp.json file and sends fixed headers on every request. Routeur needs one header, the API key as a bearer token, which Cursor can read from an environment variable so the file never holds the secret.

Configuration

File	Applies to
`~/.cursor/mcp.json`	Every project on this machine
`.cursor/mcp.json` in a repository	That project only

mcp.json

{
  "mcpServers": {
    "routeur": {
      "url": "https://api.routeur.app/mcp",
      "headers": {
        "Authorization": "Bearer ${env:ROUTEUR_API_KEY}"
      }
    }
  }
}

Remote servers are identified by url; no type field is needed. ${env:NAME} is Cursor’s interpolation syntax for environment variables (format and file locations from cursor.com/docs/context/mcp, checked on 2026-09-17). Set ROUTEUR_API_KEY in the environment Cursor is launched from; on macOS a GUI launch does not read your shell profile, so start Cursor from a terminal or set the variable at the login level.

A committed .cursor/mcp.json must never carry a literal key. If your build does not expand ${env:...}, keep the key in ~/.cursor/mcp.json and out of version control.

Verify

Open Cursor Settings > MCP (or the Customize sidebar) and toggle routeur on. The server should list its 38 tools within a few seconds; if it shows an error, the header was not sent or the key is wrong, which the server reports as 401. Then ask the agent for something the codebase cannot answer:

Using routeur, call market_snapshot for venue kalshi, id KXNFLTOTAL-26SEP17DETBUF-55 and tell me the spread, the 7-day range and the largest recent fill.

The observed result on 2026-09-17, trimmed to the fields the question needs:

{
  "price": { "yes_ask_usd": "0.52", "no_ask_usd": "0.49", "implied_chance": "0.515", "spread_usd": "0.01" },
  "history": { "days": 7, "points": 21, "low_yes_usd": "0.45", "high_yes_usd": "0.53", "change_cents": "7" },
  "recent_trading": { "recorded_fills": 200, "notional_usd": "10539.21", "largest_fill_usd": "987.27", "last_price_usd": "0.5200" }
}

Using it while you build

Routeur’s tools are useful inside a coding session as well as in chat:

Have the agent fetch a real response (get_market, list_relations, get_market_book) before it writes types for it. The shapes come from the same OpenAPI description as the API reference.
routeur://openapi.json is an MCP resource, so the agent can read the whole API description without a web fetch, and it costs no requests.
Tell the agent the API is read-only GET endpoints with decimal-string prices, graph_run on graph-derived responses, and cursor or offset pagination; point it at Errors and conventions and Pagination.
The agent’s tool calls spend your key’s quota like any other request. market_snapshot costs five; see what a tool call costs.

Any MCP client: headers, protocol versions and mcp-remote.
Tool reference: every tool the agent sees.
Reading order for LLMs: the facts to put in your project rules.

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Concepts

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Reference

Configuration

Verify

Using it while you build

Configuration

Verify

Using it while you build

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