FetchSandbox

io.github.fetchsandbox/mcp

A deterministic verification engine for agents. Proves a fix: fails on the old code, passes on new.

Yes, your AI can use this right now.Answered a live MCP handshake in 117 ms with no sign-in needed and exposes 8 tools.

Connect it

Settings → Connectors → Add custom connector
URL: https://fetchsandbox.com/mcp/v1

8 tools, verified live

Pulled straight from the server with tools/list on 2026-10-17.
coachread-only

Conversational integration coach for FetchSandbox. Server-side orchestrator that walks the user through adding an API integration (payments / email / auth / etc.) — intake the goal, elicit domain-aware discovery questions from the spec's brain.yaml, route to the right workflow, prove the contract via FetchSandbox, surface compliance notes. Call this BEFORE any other FetchSandbox tool when the us

get_jobread-only

Retrieve the SAME running find_bugs, fix_bug, prove_fix, verify_behavior or validate_integration job (including requirements planning). Follow next_tool_call until status is done or error. Never restart the original tool to poll. A proposed plan is not execution proof; a running response is not proof. Only the completed measured verdict and receipt can establish a pass.

guideread-only

ROUTE a symptom to the provider behaviour that explains it. Use this when the user names a provider or a domain (payments, email, auth, SMS, subscriptions) and you need to know what that provider ACTUALLY does — not what its docs say, and not what can be inferred from reading the integration code. Reading the code tells you what your app does with a field. It cannot tell you what the field MEANS

quickrun

Run a curated reference workflow against a KNOWN, bundled spec (stripe, clerk, descope, resend, twilio, and 50+ others) in ONE call — it spins up the sandbox by slug, so you do NOT need import_spec or a sandbox_id first. Use this when exploring the bundled provider contract: call `guide` on their prompt, then call `quickrun` with the returned spec + workflow. To reproduce a failure, pass the `sc

validate_integration

Completion rule: a request to verify an app includes its applicable failure checks without another user prompt. When verification_continuation.required is true, continue in this agent: inspect pending_checks, preserve every declared check and its assertions, implement supported actions, and rerun a fresh attempt. Stop only with measured results or concrete blockers showing the missing capability a

list_workflowsread-only

List the named, runnable workflows for a known provider slug or imported spec. Workflows are realistic multi-step API journeys (e.g. 'create customer → attach payment method → create subscription'). Known provider slugs need no import. Use this for exploration ("what can I do?", "show me the flows") OR before run_all_workflows when the user wants a SCOPED validation: list, filter by user inten

run_workflow

Execute ONE specific workflow by name and return its step-by-step trace PLUS a `share_url` — a public, replayable proof URL that renders the full timeline (every request, response, webhook event) for this run. The share_url is the canonical 'here's what happened' artifact: surface it verbatim in any reply that needs evidence (PR comments, Slack threads, blog posts, X replies). Do NOT substitute

verify_behavior

Prove a known fix survives a bug — the 'prove' half of reproduce→prove. The backend spawns a buggy AND a fixed reference handler and fires the bug_pattern's probes at both, returning the side-by-side diff (e.g. the buggy handler double-charges on a duplicate webhook, the fixed handler dedupes). Call this AFTER run_workflow reproduces a failure, when the matched bug_pattern has a simulation blo

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Try “Notion”, “Stripe”, “create invoice”, “browser”