JSON Formatter & Validator
Paste JSON to beautify, minify, and validate it. Errors are pinpointed to the line. Everything runs in your browser — nothing is uploaded.
About this tool
Validates and pretty-prints JSON using the browser's native parser, so what passes here is exactly what JSON.parse accepts in production. Parse errors are mapped back to the offending line and shown in context.
Your data never leaves the page — there is no server, no upload, and no tracking of tool inputs.
Frequently asked questions
Why is my JSON invalid even though it looks fine?
The usual culprits are trailing commas, single quotes instead of double quotes, unquoted keys, comments (strict JSON does not allow them), and curly smart quotes pasted from a word processor. NaN, Infinity, and undefined are also not valid JSON values. This tool maps the parser error back to the offending line so you can spot the exact character.
Is JSON with comments or trailing commas ever valid?
Not in standard JSON (RFC 8259), which is what JSON.parse and almost every API accepts. Comments and trailing commas belong to supersets like JSONC (used by VS Code config files) and JSON5. If a config file with comments works in one tool but fails here, that tool is using a lenient parser, not strict JSON.
Does formatting or minifying change my data?
Reformatting only changes whitespace, with two caveats inherent to JavaScript's parser: integers larger than 2^53 − 1 (Number.MAX_SAFE_INTEGER) lose precision because they are parsed as 64-bit floats, and duplicate keys in the same object are collapsed to the last occurrence. If you handle 64-bit IDs, keep them as strings.
Should I use 2 spaces, 4 spaces, or tabs for JSON indentation?
It is purely cosmetic — the parsed data is identical. Two spaces is the most common convention (npm, Prettier's default for JSON), four spaces is easier to scan in deeply nested documents, and minified output is what you want on the wire since it can cut payload size significantly.
How do I compare two JSON documents?
Format both documents the same way first so whitespace differences disappear, then diff them. For a structural comparison that understands keys and nesting rather than lines, use the JSON Diff tool on this site — it compares the parsed values directly.