Free tools for working with APIs.

Small, sharp pages for the things you need once an hour: read a broken JSON file, compare two responses, find the field a path selects. No account, no upload, no install.

• Everything runs in your browser
• Your data never leaves your device
• Fast, and free, and no account

JSON tools

Read, compare, query and reshape JSON.

• JSON formatter and validator — Format, minify and validate JSON in your browser. Line-precise errors, duplicate-key warnings, and big numbers kept exactly as written. Nothing is uploaded.
• JSON diff — Compare two JSON documents structurally. Key order and formatting are ignored, arrays can be matched by position, by id or as a set. Nothing is uploaded.
• JSONPath tester — Write a JSONPath and watch it match, with the exact path of every result. Filters, slices, unions and recursive descent, all in your browser.
• JSON flatten and unflatten — Turn nested JSON into one level of dotted keys and back again, losslessly. Export as CSV or environment lines. Runs in your browser, nothing uploaded.
• JSON size profiler — See which keys and arrays account for the bytes in a JSON payload, how much the field names alone cost, and what it weighs gzipped.
• NDJSON viewer — Read a JSON Lines file record by record. One bad line does not stop the rest, and you can filter with a word or a JSONPath. Nothing is uploaded.

More API & dev tools

These are planned but not built yet, in roughly this order. Each will get a page of its own, working the same way: paste something, get an answer, keep your data.

JWT decoder & verifier, CORS preflight simulator, HMAC signature calculator, PKCE generator, HTTP status reference, HTTP header analyser, Cache-Control explainer, OpenAPI validator, cURL to code, OpenAPI ↔ Postman, JSON to TypeScript, JSON to JSON Schema, XML & XPath, WSDL viewer, Base64 encoder / decoder, Timestamp converter.