FetchSandbox Overview
FetchSandbox is a runnable API integration sandbox designed for developers and AI coding agents. It provides a memory graph and an MCP (Model Context Protocol) server that lets your AI assistant build, test, and validate API integrations directly inside your IDE — without burning real API quotas or touching production data. Instead of stopping at successful HTTP responses, FetchSandbox verifies webhook delivery, workflow state, contracts, and real integration behavior end to end. It ships with pre-configured support for Stripe, Twilio, Resend, Clerk, Privy, AgentMail, Surge, Kulipa, WorkOS, and more, with 75 APIs available in its live catalog.
How to use FetchSandbox
Connect FetchSandbox to your IDE in about 30 seconds. It works with Cursor, VS Code, Claude Code, Windsurf, Cline, and other MCP-compatible tools. Once connected, you can run commands like ./fetchsandbox "test my stripe integration" directly from your AI coding assistant. The agent picks a failure scenario, runs it against a stateful sandbox, reproduces the bug, and returns a public receipt URL you can paste into pull requests or Slack. You can also import your OpenAPI spec and use the CLI for scripted testing.
Core Features of FetchSandbox
- MCP + CLI access: MIT-licensed packages that plug into Cursor, Claude Code, Codex CLI, Windsurf, VS Code, Cline, and more.
- Stateful API sandbox: Carries state between steps — e.g., a created customer exists for a subsequent charge — and fires the same webhooks the real API would.
- Pre-configured integrations: Stripe, Twilio, Resend, Clerk, Privy, AgentMail, Surge, Kulipa, WorkOS, plus 50+ bundled APIs on the free plan.
- Failure simulation: Duplicate webhooks, out-of-order delivery, stale events, mid-flow 401 token expiry, mid-workflow 429 rate limits, retries, and async state changes.
- Webhook verification: Confirms delivery, workflow state, and invariants defined in the run specification — not just a 200 OK.
- Receipt URLs: Public, replayable proof that can be linked in PRs and Slack.
- OpenAPI imports: Turn your spec into runnable environments without manually rebuilding docs or mocks.
- Scenario library: Guided runs that reproduce real bug patterns, such as Stripe requires_action, charge.refunded, and checkout.session.completed race conditions.
Use Cases for FetchSandbox
FetchSandbox is well suited for testing payment integrations (Stripe, Paddle), email sending and delivery webhooks (Resend, AgentMail), authentication flows (Clerk, Descope, WorkOS), and any workflow where webhook delivery and async state matter. Teams use it to reproduce production bugs deterministically, test webhook replay handling, validate idempotency logic, prove retry and backoff behavior, and review AI-generated integration code before merging. It also supports contract testing against OpenAPI specs and guided runs for brownfield repositories that already use multiple APIs.
Advantages of FetchSandbox
Compared with traditional mock servers, FetchSandbox provides deterministic, stateful, end-to-end workflow simulation. It eliminates sandbox drift because environments are generated from OpenAPI specs and behave like the real API without requiring API keys, OAuth, or partner onboarding. Developers report catching duplicate-webhook and idempotency bugs on day one, and the receipt URL system provides reusable evidence in code review. The free tier (1,000 runs/month) is genuinely free — no credit card required.
Pricing and Plans
- Free — $0 forever: 1,000 runs/month, all 50+ bundled APIs, CLI + MCP access, OpenAPI imports, community support.
- Pro — $5/month: 10,000 runs/month, pay-as-you-go at $5 per extra 10,000 runs, private integrations, webhook replay + run history, Slack/email support.
- Enterprise — Custom pricing: unlimited runs, onboard private APIs, SSO/SAML + team seats, audit logs + private storage, SLA + priority support, VPC/on-prem option.
- The MCP package and CLI are MIT-licensed and free; paid tiers cover the hosted backend.
FetchSandbox FAQ
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