CheckcraftOnline JSON validator that explains the error
Checkcraft is a desktop app for checking APIs and logs without code, with a free edition. Download, no sign-up →
JSON syntax validation right on the page. The validator does not just say “error”: it shows the spot and explains what to fix.
What the validator recognizes
Trailing commas, single quotes, unquoted field names, comments, invalid values such as NaN and undefined, numbers with leading zeros, line breaks inside strings, invalid backslashes, unclosed strings and brackets, text after the JSON, empty input, an invisible BOM and HTML instead of JSON. The Format button indents valid JSON.
Where your data goes
Nowhere. A script in your browser does the check and the page sends nothing to a server. Still, avoid pasting passwords and tokens without need.
Valid JSON is not the same as a correct response
Syntax checks only the form. An API response can be valid JSON and still hold a wrong status, total or extra fields. Values are checked with rules: on the online API response check page or in Checkcraft, where rules are saved and run on every pass.
Repeat this on your own API
Checkcraft is a desktop app that saves API response checks without code and shows what did not match. Start with a sample, then use your own sanitized data. Free runs on Windows and Linux with no time limit.
Download FreeDownload and first runNo sign-up or email needed, the archive is ready in a couple of minutes. See the edition limits.
Start with the linked example and compare its result with your own test requirement.