What is JSON?
JSON (JavaScript Object Notation) is the most popular format for sending data between apps, websites and servers. APIs return it, configuration files use it and SEO structured data (JSON-LD) is written in it. JSON is easy for machines to read, but a long single line of minified JSON is very hard for people to read. The official specification is on json.org.
This JSON formatter makes JSON readable, compact or checked for errors, all without sending your data anywhere. That matters, because JSON often contains API keys, customer data or private settings.
Features
- Format / Beautify: adds line breaks and indentation (2 spaces, 4 spaces or tabs)
- Minify: removes all spaces and line breaks for the smallest size
- Validate: tells you if the JSON is valid, and if not, shows the error with its line and column
- Sort keys A-Z in every object, useful for comparing two JSON files
- Copy or download the result as a .json file
How to use the JSON formatter
- Paste your JSON into the input box.
- Click Format / Beautify, Minify or Validate.
- If there is an error, the message points you to the problem line.
- Copy or download the result.
Common JSON errors and how to fix them
| Error | Example | Fix |
|---|---|---|
| Single quotes | {'name': 'Ali'} | Use double quotes: {"name": "Ali"} |
| Trailing comma | {"a": 1,} | Remove the last comma |
| Unquoted keys | {name: "Ali"} | Quote every key |
| Comments | // note | JSON does not allow comments |
| Missing comma | {"a": 1 "b": 2} | Add a comma between items |
JSON is stricter than JavaScript. Values can only be strings, numbers, true, false, null, arrays and objects. Things like undefined, functions and dates are not allowed. Mozilla's JSON reference explains more.
Who uses a JSON formatter?
Developers debugging API responses, SEO specialists checking JSON-LD schema, data analysts reading exports and students learning web development. If you create schema markup, generate it with our Schema Markup Generator and use this tool to tidy it. Working with encoded data? Try the Base64 Encoder and Decoder. See all text and developer tools.
JSON syntax in one minute
JSON (JavaScript Object Notation) is a text format for data. The rules are strict:
| Element | Example |
|---|---|
| Object | {"name": "Ali", "age": 30} |
| Array | ["red", "green", "blue"] |
| String | "hello" (double quotes only) |
| Number | 42, 3.14, -7, 1e6 |
| Boolean | true, false |
| Null | null |
Keys must be strings in double quotes, items are separated by commas, and there must be no comma after the last item. The full grammar is on json.org and in the standard RFC 8259.
Five errors that break JSON
- Trailing commas:
{"a": 1, "b": 2,}is invalid. Remove the last comma. - Single quotes:
{'a': 1}is invalid. Use"a". - Unquoted keys:
{a: 1}works in JavaScript but not in JSON. - Comments:
// noteis not allowed in standard JSON. - Special values:
undefined,NaNand dates likenew Date()are not valid JSON values. Store dates as strings, for example"2026-10-25".
When validation fails, the formatter shows where the problem is so you can fix it quickly.
Format, minify and sort
- Format (beautify) adds indentation and line breaks, making nested data easy to read and compare.
- Minify removes all unnecessary spaces, making the file smaller for sending over a network.
- Sort keys A-Z puts object keys in alphabetical order, which makes it much easier to compare two versions of a config file or API response.
Where developers meet JSON
JSON is everywhere in modern web work: REST API responses, configuration files like package.json, structured data (JSON-LD) for SEO, browser storage, logs and data exports. If you build schema markup, the Schema Generator produces ready-made JSON-LD you can paste and validate here. If an API returns Base64 data inside JSON, decode it with the Base64 Encoder/Decoder.
Private by design
Developers often need to check JSON that contains API keys, tokens or customer data. Pasting that into a random website is risky. This formatter runs entirely in your browser using the built-in JSON.parse and JSON.stringify functions, so the data never leaves your computer. Still, it is good practice to remove secrets before sharing JSON with anyone. The MDN JSON reference explains these functions in detail.
Example: debugging an API response
You call an API and get one long line of text that is hard to read:
{"status":"ok","data":{"user":{"id":42,"name":"Sara","roles":["admin","editor"]}}}
Paste it into the formatter and click Format. The result shows the structure clearly, with data containing a user object that has an id, a name and a list of roles. You can immediately see where each value lives and write the code to read it, for example response.data.user.roles[0].
If the API returns an error such as "Unexpected token", paste the response here and click Validate. Often the problem is an HTML error page returned instead of JSON, or a value that was cut off. Seeing the exact line and column of the error makes the bug much faster to find.
JSON vs. other data formats
JSON is not the only way to store data. XML is older and more verbose, and is still common in sitemaps, RSS feeds and many enterprise systems. YAML is popular for configuration files because it is easy for people to read, but indentation mistakes can break it. CSV is ideal for simple tables and spreadsheets. JSON sits in the middle: readable for humans, easy for every programming language, and the default for most web APIs today.
Frequently Asked Questions
Is my JSON uploaded anywhere?
No. Formatting and validation run entirely in your browser.
Can it fix my JSON automatically?
It shows exactly where the error is, but you fix it yourself. That avoids silently changing your data.
How large a file can it handle?
Several megabytes work fine. Very large files depend on your device's memory.
Does it support JSON with comments (JSONC)?
No. Standard JSON does not allow comments, so remove them first.
What is the difference between JSON and a JavaScript object?
JSON is a text format with stricter rules: double-quoted keys and strings, no functions, no comments and no trailing commas.
Why are my numbers changing?
Very large integers beyond about 9 quadrillion (2^53) lose precision in JavaScript. Store very large IDs as strings.
Can I download the formatted result?
Yes. Use Download .json to save the result as a file.
Last updated: October 25, 2026