JSON Formatter & Validator
Format, validate & fix JSON online
Beautify messy JSON, catch errors with the exact line and column highlighted, and repair common mistakes in one click — all in your browser, nothing uploaded.
🔒 100% private — your document is processed entirely in your browser and is never uploaded, logged, or stored.
A JSON formatter that shows you exactly what’s wrong
Most online tools tell you your JSON is “invalid” and leave you hunting for the problem.Indentio pinpoints the precise line and column, underlines it in red, and explains the mistake in plain English — then offers a one-click fix. It is a formatter, validator, and repair tool in a single fast page.
How to use it
- Paste or upload your JSON, or click
Sampleto try it. - Errors are underlined live as you type — hover the red mark for details and a fix hint.
- Click Format to beautify, Minify to compact, or Auto-fix to repair.
- Use Tree view to explore structure, then Copy or Download.
Common JSON mistakes it catches
- Trailing commas —
[1, 2, 3,]is valid in JavaScript but not in JSON. - Single quotes — JSON keys and strings must use
"double quotes". - Unquoted keys —
{ name: "x" }should be{ "name": "x" }. - Unclosed brackets or braces — the tool tells you the document ends too early.
- Missing commas between array items or object properties.
Why developers pick it over other formatters
- Exact error location with an in-editor red underline — not a vague message.
- One-click Auto-fix powered by a proven JSON-repair engine.
- Handles JSON and XML in the same clean, keyboard-friendly editor.
- Fully private and free, with no sign-up.
Frequently asked questions
How do I format (beautify) JSON?
Paste your JSON into the editor and click Format (or press Ctrl/⌘ + Enter). Your JSON is re-indented with 2 spaces, 4 spaces, or tabs — your choice. If anything is invalid, the exact spot is underlined in red before formatting.
What JSON errors can it detect?
Missing or extra commas, trailing commas, single quotes instead of double quotes, unquoted keys, unclosed brackets and braces, and unterminated strings — each reported with a precise line and column and a plain-English explanation.
Can it fix my broken JSON automatically?
Yes. Click Auto-fix and common problems — trailing commas, single quotes, unquoted keys, missing brackets — are repaired in place, then re-formatted. You stay in control and can review the result.
Is my JSON uploaded to a server?
No. All formatting and validation happen locally in your browser using JavaScript. Your data never leaves your device — nothing is uploaded, logged, or stored.
Is there a size limit?
There is no fixed limit. The editor is virtualized and handles large documents smoothly; very large files depend only on your device’s memory.