How to Use the Exchange Rate API MCP Server with Claude Code and Cursor

AI coding tools are great at writing code and explaining diffs, but they're unreliable at anything numeric and time-sensitive. Ask Claude Code "what's today's USD to EUR rate?" and you'll get a stale guess. The Model Context Protocol (MCP) fixes this by letting clients call real tools. This post walks through the Exchange Rate API MCP server — what it does, how to install it in four different clients, and how to debug when something goes wrong.

What is the Exchange Rate API MCP server?

It's a small npm package — @exchangerateapi/mcp-server — that exposes four currency tools over the MCP stdio transport. Any MCP-compatible client (Claude Code, Cursor, Claude Desktop, ChatGPT Desktop, and any custom MCP host) can call them:

Two of the four tools (get_exchange_rate and list_currencies) work without an API key. Set EXCHANGERATE_API_KEY for the historical and multi-target endpoints.

Prerequisites

• Node.js 18 or newer. npx ships with Node and handles installing the package on first run.
• An MCP-compatible client. Claude Code, Cursor (0.42+), Claude Desktop, or ChatGPT Desktop all qualify.
• Optional: Exchange Rate API key — register for a free one if you need higher limits.

Install in Claude Code

claude mcp add exchangerateapi -- npx -y @exchangerateapi/mcp-server
claude mcp env exchangerateapi EXCHANGERATE_API_KEY=your_key_here   # optional

Claude Code will install the package on first invocation via npx. Verify it's loaded:

claude mcp list
# should show: exchangerateapi  running  (4 tools)

Now open any chat and ask: "What's the USD to EUR rate right now?" Claude Code picks up the get_exchange_rate tool, calls it, and answers with the live number.

Install in Cursor

Edit ~/.cursor/mcp.json (or create a project-local .cursor/mcp.json):

{
  "mcpServers": {
    "exchangerateapi": {
      "command": "npx",
      "args": ["-y", "@exchangerateapi/mcp-server"],
      "env": {
        "EXCHANGERATE_API_KEY": "your_key_here"
      }
    }
  }
}

Restart Cursor. Settings → Cursor Settings → MCP should now list "exchangerateapi" with a green indicator. You can toggle individual tools there if you want.

Install in Claude Desktop (and ChatGPT Desktop)

Edit the desktop client's config file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• ChatGPT Desktop uses the same JSON shape in its own config — paste the block below.

{
  "mcpServers": {
    "exchangerateapi": {
      "command": "npx",
      "args": ["-y", "@exchangerateapi/mcp-server"],
      "env": {
        "EXCHANGERATE_API_KEY": "your_key_here"
      }
    }
  }
}

Fully quit and reopen the app. The "Search and tools" icon should show exchangerateapi with four tools.

Example prompts

A few prompts that exercise each tool:

• "What's 1,250 GBP in Singapore dollars?" — calls get_exchange_rate, multiplies client-side.
• "Show me the trend of USD/JPY over the last 30 days." — calls get_historical_rates with period=30d.
• "Get me today's rates for EUR against USD, GBP, and CHF in one call." — calls get_rates_authenticated with comma-separated targets (requires API key).
• "What currencies does Exchange Rate API support?" — calls list_currencies.

Debugging tool calls

If the assistant isn't calling the tool, or calls are failing, there are three quick checks.

1. Is the server actually running?

In your terminal:

npx -y @exchangerateapi/mcp-server
# waits on stdin — this is correct, stdio transport

Press Ctrl+C to exit. If this errors (e.g. command not found: npx), install Node 18+.

2. Send a raw tools/list request

MCP is JSON-RPC over stdio. You can drive it manually:

printf '%s\n' \
  '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"0"}}}' \
  '{"jsonrpc":"2.0","method":"notifications/initialized"}' \
  '{"jsonrpc":"2.0","id":2,"method":"tools/list"}' \
  | npx -y @exchangerateapi/mcp-server

You'll see the handshake plus a list of all tool schemas. If this works, the server is healthy — the problem is in the client config.

3. Check the client's MCP log

Claude Desktop writes a log you can read at:

# macOS
~/Library/Logs/Claude/mcp*.log

# Windows
%APPDATA%\Claude\logs\mcp*.log

Look for exchangerateapi lines. A common issue: the config's JSON is invalid (trailing comma, missing quote). The log will say so.

Do I need an API key?

Only for two of the four tools. get_exchange_rate and list_currencies call public endpoints and work without a key. get_historical_rates and get_rates_authenticated both require EXCHANGERATE_API_KEY. Set one if you want:

• Historical rate data (1d/7d/30d/1y periods).
• Multi-target single-call lookups (e.g. EUR against USD + GBP + CHF).
• Higher rate limits (the public endpoints have reasonable but not unlimited quotas).

A free key is available at registration — no credit card.

What about privacy?

The MCP server runs locally on your machine and talks to exchange-rateapi.com/api directly. It doesn't log prompts, and it doesn't proxy through a third party. Source is on GitHub — you can read it end-to-end in under 15 minutes.

Related integrations

• DeepSeek (Python): exchange-rateapi-deepseek — same tools, wired into DeepSeek's function calling.
• Any LLM with browsing: our /llms.txt tells them the public endpoint to call.
• Every supported client: the full rundown is on the MCP landing page.

Next steps

1. Install the server in your preferred client (above).
2. Ask your assistant for a live rate — confirm it cites the number.
3. If you need multi-target or higher limits, grab a free API key and set EXCHANGERATE_API_KEY.
4. Open an issue or PR on the repo if something's missing.

npm install @exchangerateapi/sdk