A mock server that lives inside the page

Most OpenAPI tools render “Try it out” buttons that fail without a real backend. In OASForge the default server is a mock implemented in the page itself — requests from Swagger UI are answered locally, instantly, offline.

Stateful, not canned

• POST to a collection path really creates a record, kept in memory
• GET lists what you created; GET /thing/{id} returns that record
• PUT/PATCH merge updates; DELETE removes — and a later GET honestly 404s
• Endpoints without stored data answer with examples derived from your response schemas ($refs resolved, formats respected)
• Everything else echoes the request back, httpbin-style, so you can inspect what was sent

Testing error paths

Two request headers steer the mock: X-Mock-Status forces any status code documented on the operation (test your 400s and 502s without breaking anything), and X-Mock-Delay adds artificial latency for spinner and timeout testing.

Why in-browser matters

Nothing to install, nothing to run, nothing to secure. Spec reviews, client demos, workshops and interviews all work from a single browser tab — or from the offline single-file build on a machine with no internet at all. A live httpbin.org server stays selectable when you want to hit something real.