JSON Formatter & Validator
Paste messy JSON to beautify it, check it for errors, or minify it for production. Your data never leaves your browser.
🔒 Runs entirely in your browser. Nothing you enter is sent to a server.
JSON (JavaScript Object Notation) is the format almost every web API speaks. But JSON straight from a server, log file or database export usually arrives as one long unreadable line. This tool turns it into neatly indented, readable structure, tells you exactly where it is broken if it won’t parse, and can squeeze it back down to the smallest possible size when you are ready to ship it.
How to use the JSON formatter
- Paste your JSON into the input box on the left, or click Try an example to see how it works.
- Pick an output style. Two-space indentation is the most common choice for config files and documentation. Four spaces or tabs suit some team style guides, and Minify strips all whitespace.
- Optionally sort keys A–Z. This makes two similar objects much easier to compare side by side.
- Copy or download the result. The output updates live as you type, so there is no button to press.
If the JSON is invalid, a red message tells you the line and column where parsing stopped. That is usually the spot right after the real mistake.
Beautify vs. minify: when to use each
| Beautified | Minified | |
|---|---|---|
| Best for | Reading, debugging, code review, docs | Network payloads, storage, embedding in code |
| Whitespace | Line breaks and indentation | None |
| Typical size | Larger | 10–30% smaller |
| Data | Identical | Identical |
Both versions contain exactly the same data. Whitespace outside of strings has no meaning in JSON, so a parser treats them identically.
The most common JSON errors (and how to fix them)
Most broken JSON comes from a handful of mistakes that are easy to make when you write it by hand or copy it out of JavaScript code:
- Trailing commas.
{"a": 1, "b": 2,}is valid JavaScript but invalid JSON. Delete the comma before the closing brace or bracket. - Single quotes. JSON strings and keys must use double quotes, so
{'name': 'Ada'}has to become{"name": "Ada"}. - Unquoted keys.
{name: "Ada"}fails. Every key needs double quotes. - Comments.
//and/* */aren’t part of JSON. Remove them, or use a format that supports them such as JSONC or YAML. - Special values.
undefined,NaNandInfinitydon’t exist in JSON. Usenullor a string instead. - Unescaped characters inside strings. A raw line break or tab inside a string must be written as
\nor\t, and a literal double quote as\".
Tip: When the error points at a line that looks fine, check the line above it. A missing comma at the end of one line is only noticed when the parser reaches the next value.
Why validate JSON before you use it?
An invalid JSON payload can take down a deploy, break a CI pipeline or make an API return a vague 400 Bad Request error. Running a file through a validator first takes seconds and points you to the exact character at fault, which is far quicker than reading a stack trace. This is especially useful for package.json, tsconfig.json, VS Code settings and infrastructure config files, where a single stray comma can stop everything.
Is this tool private?
Yes. Many online formatters send your input to a server to process it. That is a real risk when the JSON holds access tokens, personal data or internal API responses. Here, parsing and formatting happen with your browser’s built-in JSON.parse and JSON.stringify functions, so the data never leaves your machine.
Frequently asked questions
Is it safe to paste API keys or customer data into this JSON formatter?
Yes. The formatter runs as JavaScript inside your browser tab, and nothing you paste is uploaded. You can even disconnect from the internet after the page loads and it will keep working.
Why does my JSON fail validation when it works in JavaScript?
JSON is stricter than JavaScript object syntax. Keys must be wrapped in double quotes, strings can't use single quotes, trailing commas aren't allowed, and comments aren't part of the standard.
Does sorting keys change my data?
No. Sorting only changes the order keys appear in each object. The values, array order and nesting stay exactly the same, and JSON objects are unordered by definition.
How large a file can I format?
Files of several megabytes format comfortably on a modern laptop. Very large files, around 50 MB and above, depend on how much memory your device and browser have.