JSON Formatter
The JSON Formatter takes JSON text you paste or upload and beautifies it (indented), minifies it, or validates its syntax. Parsing happens in a Web Worker right inside your browser, so nothing is sent to a server — open the Network panel in DevTools to confirm. Files over 10MB format smoothly without freezing the page.
How to use it
- 1
Paste or upload JSON
Paste JSON into the editor, or drag and drop / pick a local .json file. The file never leaves your device.
- 2
Choose an indent style
Pick 2 spaces, 4 spaces or a tab in the top-right corner. Switch to Minify when you need the smallest single-line payload for transport.
- 3
Format and validate
Click Format (or press Ctrl+Shift+F) to produce beautified output. If the JSON is invalid, the offending line is highlighted and the expected token is reported.
- 4
Copy or keep going
Copy the result, or send it straight to the tree view, diff or type-generation tools without copy-pasting again.
Key features
Precise error locations
A custom mapper on top of native JSON.parse reports the exact line and column, highlights the position in-line, and explains what was expected versus what was found.
Web Worker keeps the UI alive
Parsing and formatting run on a background thread, so typing and scrolling stay responsive even with large inputs.
Handles big files
Files over 10MB use worker parsing plus viewport rendering; above 5MB the editor switches to a read-only, chunked mode automatically.
Indentation and extra operations
Supports 2/4 spaces and tabs, plus alphabetical key sorting and string escape / unescape helpers.
Safe for sensitive data
API payloads, tokens and config files you would rather not share are perfectly fine to paste here.
No ads
No ad slots or pop-ups, and no bloated third-party scripts to wait for on first paint.
Common errors & troubleshooting
- ! Error "Unexpected token } in JSON at position N" — usually a trailing comma after the last key/value pair, which the JSON spec does not allow.
- ! Error "Unexpected token '\''" — JSON strings and keys must use double quotes; single quotes are not valid.
- ! Error "Unexpected non-whitespace character after JSON" — a document can only have one root value. Wrap multiple values in an array.
- ! Comments (// or /* */) are not allowed in standard JSON. Strip them from config files before formatting.
Frequently asked questions
Does the JSON formatter upload my data to a server?
No. Formatting, minifying and validation all happen locally in your browser — there is no server involved.
What is the difference between formatting and minifying?
Formatting (beautifying) adds indentation and line breaks by nesting level so a human can read and debug the structure. Minifying removes all unnecessary whitespace and line breaks to produce compact single-line JSON that is smaller to transfer and write to production config. Neither changes the data itself.
How large a JSON file can it handle? What if it feels slow?
Ordinary payloads complete instantly; files around 10MB are parsed in a Web Worker, usually within a second and without freezing the interface. Above 5MB the editor switches to a read-only, chunked rendering mode to stay smooth. If the file contains integers larger than 2^53, enable big-number precision mode as prompted.
It says my JSON is invalid but I cannot see where. What now?
The tool highlights the line and column in-line and reports the expected token. The usual suspects, in order, are trailing commas, single-quoted strings, missing double quotes, and leftover comments. Walk through the Common errors section on this page one by one.
Is the JSON formatter free? Do I need an account?
It is free, with no sign-up, no usage limits and no ads. Future AI-powered extras may work on a bring-your-own-key basis; the local tools stay free.
Related tools
JSON Validator
Check whether your JSON is valid. Syntax errors are highlighted with the exact line and column, plus a hint about the token that was expected.
JSON Diff / Compare
Compare two JSON documents side by side. Additions, deletions and changes are colour-coded, and key or array order can be ignored.
JSON to TypeScript
Generate TypeScript interface or type definitions from a sample JSON payload.
JSONPath Query
Query JSON with JSONPath expressions, with a built-in syntax cheat sheet and one-click copy of each result.