Connecting Claude

Claude.ai and Claude Desktop (OAuth)

The easiest way: a custom connector with OAuth.

1. In Claude, go to Settings → Connectors.
2. Choose Add custom connector.
3. Enter EenFactuurMaken.nl as the name and https://eenfactuurmaken.nl/mcp as the URL.
4. Click Connect, sign in to EenFactuurMaken.nl and give permission.
5. In a chat, turn on EenFactuurMaken.nl in the tools and connectors menu.

A connector you add on claude.ai also works in Claude Desktop. Whether custom connectors are included in your plan is explained by Anthropic.

Claude Desktop with an API key

Prefer an API key? In Claude Desktop open Settings → Developer → Edit Config and put this in claude_desktop_config.json:

{
  "mcpServers": {
    "eenfactuurmaken": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://eenfactuurmaken.nl/mcp", "--header", "Authorization:${EENFACTUURMAKEN_AUTH}"],
      "env": { "EENFACTUURMAKEN_AUTH": "Bearer efm_your_key" }
    }
  }
}

Then restart Claude Desktop. This needs Node.js: mcp-remote connects Claude Desktop to our server. The key lives in env so the space in "Bearer …" also works on Windows.

Claude Code

One command in your terminal. With OAuth (no header):

claude mcp add --transport http eenfactuurmaken https://eenfactuurmaken.nl/mcp

Then type /mcp in Claude Code, choose eenfactuurmaken and Authenticate. Your browser opens so you can sign in.

Or with an API key:

claude mcp add --transport http eenfactuurmaken https://eenfactuurmaken.nl/mcp \
  --header "Authorization: Bearer efm_your_key"

You can also set up the server per project in .mcp.json:

{
  "mcpServers": {
    "eenfactuurmaken": {
      "type": "http",
      "url": "https://eenfactuurmaken.nl/mcp",
      "headers": { "Authorization": "Bearer ${EENFACTUURMAKEN_API_KEY}" }
    }
  }
}

Put the key in the EENFACTUURMAKEN_API_KEY environment variable and not in the file, especially if you commit it to git.

Try it

Ask for example: "Show my outstanding invoices" or use the create-invoice prompt from the prompt menu. See All tools.