Connect your agent. Check what actually happened.

We started with API-heavy teams.

Retries, delayed events, and partial failures exposed the gap between a successful request and a correct system. That was our starting point. The question applies to jobs, queries, services, and application code too.

If your use case is different, bring it to us. We’ll work with your team to define what must stay true, what failures to exercise, and what evidence you need. The free engine’s existing integration coverage is a starting point, not a claim that every system is already supported.

Local agents: connect with npx.

Use this stdio configuration in clients that accept an MCP JSON file. Claude Code uses a project .mcp.json or claude mcp add; Cursor supports .cursor/mcp.json or ~/.cursor/mcp.json. Other clients may use their own configuration format.

This is the tested Cursor configuration for Homebrew on Apple Silicon Mac. Run command -v npx and replace the command with your own full path if it differs. On Windows, use where.exe npx to locate your installed command. Replace fsk_your_key_here with a real key from your keys page, without a Bearer prefix. The placeholder does not authenticate.

{
  "mcpServers": {
    "fetchsandbox": {
      "command": "/opt/homebrew/bin/npx",
      "args": ["-y", "[email protected]"],
      "env": { "FETCHSANDBOX_API_KEY": "fsk_your_key_here" }
    }
  }
}

Save one FetchSandbox entry in ~/.cursor/mcp.json, check for a conflicting project entry, then fully quit and reopen Cursor. A window reload may retain the old MCP process. Enable the server in Cursor’s MCP settings if needed and confirm its tools appear.

For Codex, configure [mcp_servers.fetchsandbox] in ~/.codex/config.toml with the same command and arguments. Replace the placeholder with your account key from the keys page. Local tools can load without a key, but verification calls require authentication; the local server can also guide you through sign-in. Keep the key out of chat and source control. If Cursor on Mac cannot find npx, run command -v npx in Terminal and use that full path as the command. Follow the setup page for client-specific steps.

Hosted builders: use the HTTPS connector.

Replit and Lovable connect to the hosted MCP endpoint instead of starting a local process.

https://fetchsandbox.com/mcp/v1

Where the connector asks for authentication, choose Bearer token or API key and use your FetchSandbox account key from your keys page. This account key is separate from temporary credentials issued during a test. Keep credentials in the platform’s supported secret storage.

A connected tool is not a verified application.

Describe the change and what must stay correct. The agent should establish whether the current tools can measure it. For the available app integration checks, validate_integration prepares a session and tests the running app. A provider demonstration alone does not prove your code.

Hosted tools do not have your project’s local filesystem. Code-reading and local repair tools require a local connection. Inspect the recorded result, resolve missing evidence, and clean up temporary test configuration afterward.

Need verification beyond the available engine?

Tell us about the PR, job, database change, service, or component your team needs to trust. We’ll agree on a scope and build the verification around your system.