What teams build with Gostly

Stripe, OpenAI, Twilio, and other usage-priced services turn every CI run into a line item on next month's bill. Recording one good response and replaying it forever changes the math: per-run cost goes to zero and your test suite stops being throttled by third-party rate limits.

Gostly captures real responses once, scrubs sensitive data, and serves them locally on subsequent runs. Your code calls the same URLs — the proxy answers instead of the upstream.

The hardest bugs are the ones that depend on a specific upstream response shape: a malformed timestamp, a 207 multi-status, an empty array where you expected null. By the time you're debugging, the upstream has moved on and the response is gone.

Gostly can capture upstream responses on production-shaped traffic, scrub them, and replay them deterministically against your local build. The bug becomes a single command instead of a guessing game.

Real integration tests usually need real services, which means CI runs need credentials and network access to environments most engineers shouldn't touch. The compromise — mocking by hand — drifts from production behavior the moment the upstream changes.

Gostly closes the gap. Record realistic traffic from any non-prod environment once, commit the scrubbed library, and every PR runs the same integration paths against the same data with no production access required.

When two teams design an API together, the front end needs something to call before the back end is finished. Hand-written mocks drift; OpenAPI stubs miss real-world quirks; coordination meetings stack up.

Use Gostly to seed mocks from the API spec or a single real response, then swap in real recordings the moment the implementation is up. The contract stays in code, not in a doc.

Onboarding a new engineer usually means either giving them production credentials (uncomfortable) or pointing them at a half-working dev environment (frustrating). Both options cost the team time and create risk.

A pre-recorded mock library gives new engineers a realistic system to learn against on day one — same shapes, same edge cases, same scale of data — without any production credentials, network access, or way to break a live system.

Agent development chews through API quota in dev and CI. Each iteration on a prompt fires real OpenAI or Anthropic calls. Each test run renews the bill. And the responses aren't deterministic anyway, so the same input today yields a different observation tomorrow.

Record one agent run against the real upstream. Replay it forever in CI. The agent sees the same response to the same request every time — no tokens spent, no rate limits hit, no flake from upstream drift.

Integration tests against payment, identity, and messaging sandboxes look reliable until they aren't. Sandbox APIs return slightly different shapes between Tuesday and Wednesday. Sandbox quotas exhaust mid-pipeline. POSTs sometimes leak mutations to production-adjacent state.

Record a real sandbox session once. Replay it byte-for-byte in CI. POSTs return the recorded response without making the real call — your test doesn't charge a card, doesn't send a text, doesn't open a verification session that someone has to clean up.

Root-causing a third-party incident means reproducing the exact upstream sequence that triggered the failure — the same status codes, the same headers, the same body shapes, in the same order. By the time the postmortem starts, the upstream has moved on.

If the proxy was capturing traffic during the incident window, the sequence is in the recording log. Replay it locally. Step through your service against the same upstream behavior that caused the failure. The bug becomes reproducible.

Hand-written mocks go stale. Contract tests miss drift unless someone re-pulls the spec. The diff between what the upstream returned last week and what it returns this week is a manual exercise — until a test breaks in production-shaped ways and nobody knows why.

Re-record nightly. Diff the new recording against last week's. Drift surfaces as a report — new fields, removed fields, status changes, header shifts — before your tests have to root-cause it.