OnlineCodeEditor

JSON editor and validator

Paste or drop a JSON file. Errors are underlined at the exact position the parser stopped, and Run shows a summary of the structure.

Loading the editor…

Strict JSON, honestly reported

Validation uses the browser’s own JSON.parse, so what passes here will parse in JavaScript. Comments, trailing commas and single quotes are reported as errors rather than silently accepted. Large objects can be folded from the gutter, and the outline lists top-level keys.

Format, minify, compare

Shift+Alt+F formats with Prettier. The code minifier page compacts JSON to a single line. Save a snapshot with Ctrl/Cmd+S before a big edit and compare it later from Local history.

JSON Schema validation is not included; a schema that references remote URLs would need network access, which this editor does not use.

How to use it

  1. Remove a comma and watch the error marker.
  2. Press Run to see the top-level type, key count and depth.
  3. Format with Shift+Alt+F.

Questions

Does it accept JSON with comments (JSONC)?

No. Comments are reported as errors because standard JSON parsers reject them.

How big a file can I open?

Files up to 5 MB import fine; diagnostics are skipped above 2 MB to keep typing responsive.

Is my JSON sent to a server?

Never. Parsing, formatting and saving happen in your browser.