JSON Formatter / Validator

Make JSON readable and catch invalid payloads before they reach production

JSON is the interchange format of the web, but the payloads you actually debug rarely arrive pretty-printed. API responses come back as one long line, config files mix tabs and spaces, and a single stray comma makes an entire document unparseable. This tool solves both halves of that problem: it validates your JSON against the strict grammar and formats it with consistent indentation, so you can read nested structures at a glance and trust that what you ship will parse.

You need it any time a fetch call fails, an API returns a cryptic parse error, or you inherit a minified config file. Because validation runs locally in the browser, nothing you paste ever leaves your machine.

Validate and Pretty-Print in Six Steps

1. Paste the raw JSON — minified, indented, or copied from a network tab — into the input area.
2. Click Validate. The tool reports success or pinpoints the exact line, column, and character where parsing stopped.
3. Read the error message, which names the offending token, such as an unexpected , or a missing closing brace.
4. Fix the reported position, then validate again until the document is clean.
5. Switch to the formatted view to apply two-space indentation to every nested object and array.
6. Copy the formatted result back into your editor, or use the minified view to shrink it for storage or transfer.

Real Example: A Trailing Comma That Breaks Parsing

Trailing commas are legal in JavaScript object literals but illegal in JSON. A config file ending with "retries": 3, parses fine in your head but fails in every strict JSON parser, producing an error like Unexpected token ,. The validator flags the exact character so the fix is a two-second delete rather than a hunt through a 400-line file.

Tips for Accurate Validation

• Quote every key — bare keys like name: are YAML-isms; JSON requires double quotes around both keys and string values.
• Use single quotes only for strings that contain them — JSON accepts only double-quoted strings, so escape inner quotes with \" instead of swapping quote styles.
• Validate after every edit — validate early and often while building config templates, not once at the end.
• Check numbers closely — leading zeros, hex literals, and trailing dots are all invalid JSON number syntax.
• Prefer the formatted output for diffs — pretty-printed JSON makes code reviews and merge-conflict resolution dramatically easier.

When to Reach for This Tool

• API debugging — pretty-print a response body from a network inspector to trace nested fields.
• Config authoring — validate package.json, VS Code settings, or CI pipeline definitions before committing.
• Data migration — confirm an export file is well-formed before loading it into a database or ETL job.
• Payload shrinking — minify JSON to cut bytes in logs, caches, or message queues.

Frequently Asked Questions