Using Cursor with MonoRouter: Full IDE Integration

Cursor is one of the most popular AI-powered code editors, and it works with MonoRouter out of the box. Instead of paying for Cursor's built-in AI credits or a separate API key, you can route Cursor's Claude requests through your existing subscription.

Step-by-Step Setup

1. Open Cursor Settings

Press Cmd+, (macOS) or Ctrl+, (Windows/Linux) to open Settings, then navigate to Cursor Settings → Models.

2. Add MonoRouter as a Custom Provider

Under OpenAI API Key or the Anthropic section, configure:

API Key:      mr_live_abc123
Base URL:     https://api.monorouter.dev/v1

Alternatively, you can set these in Cursor's settings.json:

{
  "cursor.aiProvider": "anthropic",
  "cursor.anthropicApiKey": "mr_live_abc123",
  "cursor.anthropicBaseUrl": "https://api.monorouter.dev/v1"
}

3. Select Your Model

In Cursor's model picker (bottom-right corner of the chat panel), select the Claude model you want:

• Claude Sonnet — best balance of speed and quality for most coding tasks
• Claude Opus — maximum reasoning power for complex architecture and debugging
• Claude Haiku — fastest responses for simple completions and edits

4. Verify the Connection

Open Cursor's chat panel (Cmd+L) and send a test message:

What model are you, and what API endpoint are you connected to?

Claude should respond. If you see an error, check the troubleshooting section below.

What Works

Everything Cursor does with Claude works through MonoRouter:

• Tab completions — inline code suggestions as you type
• Chat (Cmd+L) — ask questions about your code, get explanations
• Composer (Cmd+I) — multi-file edits with natural language instructions
• Terminal (Cmd+K) — generate terminal commands from descriptions
• Fix in Chat — send lint errors and type errors directly to Claude

Cursor uses the same Messages API that MonoRouter proxies, so there's no compatibility layer needed. Tool use, streaming, and multi-turn conversations all work natively.

Verifying from the Terminal

You can confirm MonoRouter is receiving requests by checking your dashboard, or by running a quick curl:

curl -s https://api.monorouter.dev/v1/messages \
  -H "x-api-key: mr_live_abc123" \
  -H "content-type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 64,
    "messages": [{"role": "user", "content": "Say hello from MonoRouter"}]
  }' | python3 -m json.tool

If you get a JSON response with Claude's reply, your API key and endpoint are working.

Model Selection

When you select a Claude model in Cursor (Sonnet, Opus, Haiku), that model selection is passed through to MonoRouter and then to Claude. You get the same model you'd get with a direct API key.

Performance

Cursor's inline completions are latency-sensitive — you notice if they're slow. Through MonoRouter, the added latency is minimal. First-token latency is consistently under 100ms above what you'd see with the direct API. For chat and composer interactions, the difference is imperceptible.

Troubleshooting

"Invalid API Key" error

Double-check your key starts with mr_live_ and that you've set it in the correct field. Cursor has separate fields for OpenAI and Anthropic keys — make sure you're configuring the Anthropic one.

Responses are slow or timing out

Check your MonoRouter dashboard for session health. If all sessions show as "disconnected," you may need to reconnect your Claude accounts. Also increase Cursor's request timeout in settings:

{
  "cursor.requestTimeout": 120000
}

"Model not found" error

Make sure you're using a valid model ID. Cursor sometimes uses its own model aliases. If Cursor sends claude-3-5-sonnet, MonoRouter will resolve it. But if it sends an unrecognized model string, you'll get an error.

Chat works but Tab completions don't

Tab completions use a faster, lower-latency path. If your MonoRouter session pool is under heavy load, completions might time out before chat requests do. Try adding another Claude account to your session pool.

Cost Impact

Cursor's Pro plan includes limited AI usage. Heavy users hit the cap and either wait for it to reset or pay for additional credits. With MonoRouter, your Cursor usage is bounded by your Claude subscription limits, not Cursor's usage caps. For developers who live in their IDE, this can be a significant savings.

A typical heavy Cursor user generates 500-1,000 API requests per day across completions, chat, and composer. Through the Anthropic API, that's roughly $5-15/day in token costs. Through MonoRouter, it's covered by your existing subscription.