Braintrust MCP Extension for Cursor

A Cursor extension that automatically connects the Braintrust MCP server, giving Cursor's AI assistant access to your Braintrust projects, experiments, and logs.

Prerequisites

• Cursor
• A Braintrust API key

Installation

Install from the Cursor extension marketplace:

1. Open Cursor
2. Go to Extensions (Cmd+Shift+X / Ctrl+Shift+X)
3. Search for "Braintrust"
4. Click Install

Setup

1. Set your API key

The extension reads your API key from the BRAINTRUST_API_KEY environment variable. Set this before launching Cursor.

macOS / Linux

Add to your shell profile (~/.bashrc, ~/.zshrc, etc.):

export BRAINTRUST_API_KEY="your-api-key-here"

Then restart your terminal and Cursor.

Windows

Set the environment variable via System Properties > Environment Variables, or in PowerShell:

[Environment]::SetEnvironmentVariable("BRAINTRUST_API_KEY", "your-api-key-here", "User")

Then restart PowerShell and Cursor.

2. Add Braintrust as a trusted domain

To allow the extension to authenticate without OAuth prompts:

1. Open Cursor Settings (Cmd+, / Ctrl+,)
2. Search for "trusted domains"
3. Add braintrust.dev to the list of trusted domains
4. Restart Cursor

Usage

Once the extension is installed and BRAINTRUST_API_KEY is set, the Braintrust MCP server is automatically registered when Cursor starts. No manual steps required.

Troubleshooting

"BRAINTRUST_API_KEY is not set"

• Verify the variable is set: echo $BRAINTRUST_API_KEY (macOS/Linux) or echo %BRAINTRUST_API_KEY% (Windows)
• Cursor must be restarted after setting environment variables
• On macOS, launching Cursor from Spotlight/Dock may not inherit shell variables — launch from terminal instead

Extension doesn't seem to work

• This extension only works in Cursor, not vanilla VS Code
• Ensure you're running a recent version of Cursor that supports the MCP Extension API

Contributing

See CONTRIBUTING.md for development setup and build instructions.

License

MIT