Viktor.comAn AI coworker that actually does the work
Most API tests stop at 200 OK. FetchSandbox lets developers and AI agents verify what happens next—webhooks, retries, state changes, async workflows, and failure scenarios. It reproduces the real bug, proves the fix, and remembers what breaks—so your agent catches it before production. Connect via MCP to Cursor, Claude Code, Windsurf, VS Code, and Codex. Explore 60+ APIs—Stripe, GitHub, Clerk, Resend, Twilio, Descope, OpenAI—without burning real API quota or waiting on staging.
This is the 2nd launch from FetchSandbox. View more
FetchSandbox MCP
Launching today
Your agent's integration fix passes CI. The data is still wrong. FetchSandbox MCP reproduces the real failure on your code, fixes it, and proves the fix held. A receipt, not a vibe. 70+ API sandboxes. One config block in Cursor or Claude Code.
Free
Launch Team / Built With
FetchSandbox
Raj here, one of the co-founders.
Writing the integration stopped being the hard part. Checking that it actually works is the whole job now, and that's the half your agent can't do.
The gap
Your agent can write a Stripe integration. It can't run one. It writes the code, tells you it's done, and you find out in production whether that was true. FetchSandbox gives the agent already in your editor two things it doesn't have: somewhere real to run integration code, and a way to prove the fix worked.
Why the proof check matters
A customer paid for 5 seats. A retry gave them 10, then 15. An agent fixed it, and after the fix nobody got any seats at all. Tests still passed because the duplicates were gone. Almost any fix makes the error disappear. Far fewer make the data right.
So the gate asserts the exact end state a correct implementation leaves, and refuses to go green when it can't reproduce the bug first.
Setup
One block in your MCP config. No API key, no signup. Works in Claude Code, Cursor, Cline, Windsurf, and Codex. 70+ ready-made sandboxes: Stripe, HubSpot, Clerk, Resend, Twilio and more, free to try.
We hit #3 on our first launch. The ask afterward was exactly this: don't just give me a sandbox, tell me my fix actually worked. This is that.
Has your agent ever confidently fixed something that was still broken?
FetchSandbox
Install, takes about thirty seconds.
Add this to your MCP config. That's `.mcp.json` in your project root for Claude Code, or Settings → MCP for Cursor:
```json
{
"mcpServers": {
"fetchsandbox": {
"command": "npx",
"args": ["-y", "fetchsandbox-mcp@latest"]
}
}
}
```
No API key, no signup. Claude Desktop needs a full quit and reopen, Cmd+Q, not just closing the window.
Try it without touching your own code first
Type this to your agent, not your terminal — the ./fetchsandbox prefix is just how you tell it to use the MCP:
"./fetchsandbox Test my Stripe webhook for duplicate deliveries"
Takes about a minute and you'll get a receipt URL.
Or the one I'd show a skeptic:
"./fetchsandbox Paddle events arrived out of order and reactivated a paused subscription"
Then point it at something real
Name the API and what you're seeing:
"./fetchsandbox Stripe webhook signature verification fails for valid events"
@rnagulapalle giving the coding agent an actual sandbox environment to fail against before calling a PR ready is a massive unlock. Congrats on the launch🙌