Green CI needs a receipt.

FetchSandbox MCP turns an AI-written API integration into a before-and-after check. The product's Product Hunt launch page describes one MCP server, 70+ API sandboxes, and a setup block for Cursor or Claude Code. 1

The mechanism is a stateful workflow. The agent can run resource creation, confirmation, webhook delivery, retries, and final-state checks, then inspect the trace instead of trusting a passing request. 2

The proof page uses a Stripe retry example: a buggy flow moves seats from 5 to 10 to 15; a correct fix keeps the state at 5 to 5 to 5. The gate also runs a deliberately broken version. A green result therefore depends on the correct end state and on a check that can fail. 3

The boundary matters. FetchSandbox is a fast preflight loop while an integration is being built. The official overview says provider sandboxes still handle final validation, while FetchSandbox supplies repeatable feedback from an IDE, CLI, or API. 2

The practical shift is small and useful: an AI agent's sentence saying "fixed" becomes a workflow, a measured state change, and a receipt another person can inspect. 3