Your agent says it works. Prove it.
FetchSandbox is the verification layer for AI agents. It executes the actions your agent takes, makes the things they depend on misbehave the way real ones do, and verifies the output — the same run has to fail before the fix and pass after. The verdict is an exit code, not an opinion.
No live provider keys. Your code stays where it is.
Runs inside Cursor, Claude Code, Codex, Lovable and Windsurf · Browse the API catalog
One run, end to end
“Connecting real testing scenarios — webhooks, retries, async state — via MCP straight into Cursor/Claude Code instead of a separate dashboard is the part that actually saves time day to day.”
“A claim that's falsifiable by the customer in 30 seconds. The before/after receipt is the trust unlock.”
“Baking the precondition into the scenario spec means the test is deterministic — and you can actually explain why it failed. The right call for v1.”
“The reliability check moves inside the agent's loop instead of being bolted on after — not a human remembering to click replay.”
“Ask only when undoing the wrong branch would cost you — and say what you already ruled out, so the question reads as work done, not helplessness.”
“Connecting real testing scenarios — webhooks, retries, async state — via MCP straight into Cursor/Claude Code instead of a separate dashboard is the part that actually saves time day to day.”
“A claim that's falsifiable by the customer in 30 seconds. The before/after receipt is the trust unlock.”
“Baking the precondition into the scenario spec means the test is deterministic — and you can actually explain why it failed. The right call for v1.”
“The reliability check moves inside the agent's loop instead of being bolted on after — not a human remembering to click replay.”
“Ask only when undoing the wrong branch would cost you — and say what you already ruled out, so the question reads as work done, not helplessness.”
“The chaos-order webhook testing is a nice touch — exactly the kinds of issues that are hard to reproduce consistently.”
“This earned its keep on day one. I pointed it at my invoice.paid handler and the duplicate-webhook run called my exact sin — dedup was a check-then-add, not an atomic primitive.”
““Not gonna pretend it's there when it's not” — most people would've said “yes, roadmap!” and I'd have quietly closed the tab. It moved you up my list.”
“This truly is the Postman for testing integrations.”
“The worst production bugs look completely fine until a second system reacts — your code passes, the API returns 200, and three hours later a duplicate webhook fires and someone gets charged twice.”
“The chaos-order webhook testing is a nice touch — exactly the kinds of issues that are hard to reproduce consistently.”
“This earned its keep on day one. I pointed it at my invoice.paid handler and the duplicate-webhook run called my exact sin — dedup was a check-then-add, not an atomic primitive.”
““Not gonna pretend it's there when it's not” — most people would've said “yes, roadmap!” and I'd have quietly closed the tab. It moved you up my list.”
“This truly is the Postman for testing integrations.”
“The worst production bugs look completely fine until a second system reacts — your code passes, the API returns 200, and three hours later a duplicate webhook fires and someone gets charged twice.”
Most API tests stop at successful responses.
FetchSandbox verifies webhook delivery, workflow state,
contracts, and real integration behavior — before production.
Your agent stops shipping integrations that “work” in tests but break in production. Every workflow run includes the spec of what success looks like — terminal state, required webhook events, invariants — verified end-to-end.
Api Request
Webhook Sent
Validation
State Verified
Production SafeBuild and test APIs without complex setup
Connect your tools, test real API workflows, and ship integrations with confidence.
Connect
Add FetchSandbox to your IDE and start testing APIs in minutes. Works with Cursor, VS Code, Claude Code, Windsurf, and more.
Run
Simulate real API behavior like webhooks, retries, failed requests, and async events. No mock servers. No complicated setup.
Ship
Generate reliable integrations using real API responses and verified workflows. Ship faster with fewer production issues.
Most API tests stop at successful responses.
Run complete workflow simulations with live events, edge cases, and failure states in one sandbox.
pick a failure → the agent runs it, asks to proceed, reproduces the bug, and hands back a receipt
Powering the Next Generation of API Development
Used to test webhooks, retries, async workflows, and production-ready integrations.
Frequently asked questions
Everything you need to know about testing APIs, simulating workflows, and shipping reliable integrations with FetchSandbox.
From API request to production ready integration.
Build, test, and validate API integrations in realistic environments before deployment. Catch failures early, reduce debugging time, and ship with confidence.