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FetchSandbox
FetchSandbox

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Runnable API integration workflows from your favorite IDE

#mcp #openapi #api #testing

AI coding agents are getting good at reading docs and writing integration code.

But API integrations still fail in the workflow.

create resource -> confirm state -> receive webhook -> fetch final state -> handle failure
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That is why I have been building FetchSandbox MCP: runnable API integration workflows from your favorite IDE.

The goal is simple. If you are already working in Claude, Cursor, Codex, Continue, or another MCP-compatible IDE, your agent should be able to run the API workflow while it is helping you integrate it.

Not just read the docs.

Run the workflow.

Inspect the response.

Check the state transition.

Verify the webhook behavior.

Then use that proof while changing your app.

Here is the raw demo:

https://www.youtube.com/watch?v=Iafkt01GAbA

What you configure

FetchSandbox MCP runs as a local MCP server using npx.

For Claude Desktop, add this to:

~/Library/Application Support/Claude/claude_desktop_config.json
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For Cursor, add this to:

~/.cursor/mcp.json
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For Claude Code, use:

~/.claude/settings.json
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or a project-level .mcp.json.

The config is the same basic shape:

{
  "mcpServers": {
    "fetchsandbox": {
      "command": "npx",
      "args": ["-y", "fetchsandbox-mcp"]
    }
  }
}
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After adding it, restart your IDE. In Cursor, also enable the new fetchsandbox MCP server in Settings -> MCP Servers.

You can also install FetchSandbox trigger-phrase skills:

curl -sL https://fetchsandbox.com/skills/install.sh | bash
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Then your IDE can respond to phrases like:

validate this integration with fetchsandbox
fs validate
check api integration coverage
validate my stripe integration
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What you can ask your IDE

Once the MCP server is connected, you can ask practical integration questions, not just documentation questions.

For an existing app:

Use FetchSandbox to validate this Stripe integration. Run the available workflows, compare the expected terminal state and webhook events, then tell me what code paths in this repo need changes.
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For a new integration:

I want to add a Stripe payment flow to this app. Use FetchSandbox to discover the runnable workflows first, then guide the implementation step by step.
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For debugging:

Run the checkout/payment workflow in FetchSandbox and inspect the failing step. Compare the expected response, state transition, and webhook events with my current implementation.
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For coverage:

Check API integration coverage with FetchSandbox and write a markdown report I can commit to this PR.
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That last flow is important. The agent can produce a local artifact like:

.fetchsandbox/validation-<date>.md
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with workflow results, step traces, acceptance criteria, terminal states, required webhook events, and invariants.

Why this is different from a mock server

A mock server can answer a request.

A guided workflow answers a better question:

Did the integration behavior actually work end to end?
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For example, a payment workflow is not just POST /payment_intents.

It is closer to:

create customer
create payment intent
confirm payment
capture payment
verify webhook
retrieve final state
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If your agent only sees endpoint examples, it can still generate code that compiles but misses the lifecycle.

If your agent can run the workflow, it has execution context.

Where FetchSandbox fits

FetchSandbox turns OpenAPI specs into:

  • stateful sandboxes
  • realistic seed data
  • lifecycle state machines
  • auth simulation
  • guided workflow runners
  • webhook behavior
  • generated developer portals
  • MCP tools for IDE agents

The point is not to replace final provider sandbox testing.

The point is to give developers and agents a fast preflight loop while the integration is being built.

Your agent can ask:

what workflows exist?
run this workflow
what state changed?
which webhook was expected?
what failed?
what should I change in the app?
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That is the developer experience I want: guided API integration workflows from the IDE you already use.

Try FetchSandbox:

https://fetchsandbox.com

Watch the demo:

https://www.youtube.com/watch?v=Iafkt01GAbA

If you build API integrations, I would love feedback on the developer flow: should agents be able to run guided API workflows directly from the IDE?

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