Free JSON Formatter and Validator
Paste JSON below to format, validate, or minify it. Everything runs in your browser — nothing is uploaded.
JSON is stricter than it looks
JSON's syntax comes directly from JavaScript object and array literals, which is where the name comes from — but despite the name, JSON itself is a language-independent data format (standardized as RFC 8259 / ECMA-404) parsed natively by virtually every modern language, not just JavaScript. The catch is that JSON is a deliberately stricter subset of JavaScript's object syntax: every key must be a double-quoted string, trailing commas are forbidden, and there's no support for comments, functions, undefined, or single-quoted strings — all things a plain JavaScript object literal allows. Code copied straight from a .js file often needs small edits before it validates as JSON.
Why formatting matters
API responses and minified config files often arrive as a single unbroken line of JSON, which is fast to transmit but painful to read or debug by eye. Formatting re-introduces indentation and line breaks purely for humans; minifying does the reverse, stripping every non-essential character to shrink the payload for storage or network transfer. Both represent the exact same data — only whitespace changes.
Frequently Asked Questions
Is my JSON uploaded to a server?
No. Formatting, validation, and minification all run entirely in your browser with JavaScript. Your data never leaves your device.
What does "Validate" check?
It checks that your input is syntactically valid JSON per the JSON specification (RFC 8259) — balanced brackets, quoted keys, valid values, and no trailing commas. If it fails, the error message shows where the problem is.
What is the difference between Format and Minify?
Format pretty-prints JSON with indentation and line breaks so it is easy to read. Minify removes all unnecessary whitespace to make the payload as small as possible for transmission or storage.
Why does my JSON fail with a trailing comma error?
Unlike JavaScript object literals, the JSON specification does not allow a comma after the last item in an object or array. Remove the trailing comma and validate again.
Can JSON contain comments?
No — the JSON specification has no comment syntax at all, so a // or /* */ comment pasted from JavaScript will fail validation. If you need annotated config, look at JSON5 or JSONC, which are supersets that add comments but aren't standard JSON.
Is a JavaScript object literal the same as JSON?
Not quite — JSON is a stricter subset. Object literals allow unquoted keys, single-quoted strings, trailing commas, and comments; valid JSON requires double-quoted keys, disallows trailing commas, and has no comment syntax at all. Code that runs fine as a JS literal can still fail JSON validation.
Is there a size limit?
There is no hard limit — because processing happens locally, the practical limit is your browser's memory. Files of several megabytes format without issue.