JSON Studio and Mock API Builder

Yes, with no usage limits, no premium tier and no account. The tools are open to everyone.

Formatting, validating, diffing and converting all run in the page, and none of that is transmitted. Two things do leave your machine, and both are buttons you press: Fix with AI sends the text to a model provider, and Share uploads a copy so the link works for whoever you send it to. Treat anything you share as readable by anyone holding the link, and do not paste credentials into either.

The formatter, validator, diff and converters work offline once the page has loaded. Fix with AI and Share need a network connection, since one calls a model and the other stores a copy.

Standard JSON (RFC 8259), JSON5 for lenient parsing, JSON Schema draft 2020-12, draft-07, draft-06 and draft-04 for validation, and YAML 1.2 for conversion. CSV output follows RFC 4180.

It builds multi-endpoint REST APIs in the browser. Define GET, POST, PUT and DELETE endpoints with path parameters, conditional responses, dynamic templates and Faker.js data, then share the whole API from a single URL with no server to run.