FetchSandbox MCP

FetchSandbox's core idea is genuinely narrow and that is its strength. It doesn't try to be a general test runner or a load testing tool. It asks one question — does this integration still do what you expect after a change — and it answers it with a binary verdict backed by a receipt that names the version tested, the observed state, and what remains unverified. The refundable part is the before/after precondition: a fix only counts when the same scenario fails on the old code and passes on the new. That single rule eliminates the most common false positive in API testing, which is a test that passes because it never exercised the failure path. The scenario model is where it earns its keep. A run is a whole workflow, not a single call. A Stripe accept_payment run creates a customer, attaches a card, charges it, and catches the webhook — with state carried between steps so the customer exists for the charge. Failure injection covers the cases unit tests skip: duplicate, out-of-order, and stale webhooks, 4xx/5xx errors, rate limiting, retries, and async state passed between steps. One customer testimonial from the vendor's site puts it plainly: pointing it at an invoice.paid handler surfaced a duplicate-webhook bug where dedup was a check-then-add rather than an atomic primitive. The distribution choice matters as much as the engine. Shipping as an MCP server and CLI that run inside Cursor, Claude Code, Codex CLI, VS Code, and Windsurf means the agent that wrote the fix also runs the check, instead of a human remembering to click replay in a separate dashboard. The MCP and CLI are MIT-licensed, so the interface layer is auditable and the paid part is the hosted sandboxes and webhook simulation. Where it doesn't fit: it tests against isolated sandboxes with representative test data, not live production data or real provider quotas. If your diligence depends on reproducing an exact production payload, this won't do it. It assumes an MCP-compatible agent or command-line workflow already exists. Self-hosted deployment, SSO, and audit are Enterprise-only. The vendor itself says it started with API-heavy teams and is extending the engine with pilot teams toward services, jobs, queries, and application code — meaning outside API integrations, you are on the roadmap rather than the product.