JSON Formatter
Paste JSON and it is formatted and checked right away.
Formatting and checking happen on this page only. Your JSON is never sent anywhere.
How to use
- 1. Paste JSONPaste it on the left or open a file (.json and similar). It is formatted and checked as you paste.
- 2. Choose the layout2 or 4 spaces, tabs, or one line (minify). You can also sort keys by name.
- 3. Copy or saveCopy the result or save it as .json. If there is an error, jump to the exact spot and fix it.
Common errors and fixes
| Message | Usual cause |
|---|---|
| A comma (,) is needed | The comma at the end of the previous line is missing |
| Trailing commas aren’t allowed | There’s a comma after the last item (“Repair” fixes it) |
| Use double quotes | Strings are in single quotes, as in JavaScript (“Repair” fixes it) |
| Keys need double quotes | A key has no quotes |
| Comments aren’t allowed | There are // or /* */ comments (“Repair” removes them) |
The JSON rules
JSON is defined by RFC 8259: strings and keys use double quotes, comments aren’t allowed, and there’s no comma after the last item. This tool checks exactly against these rules.
Sources: RFC 8259 (the JSON standard)
FAQ
Who is this for?
Developers who want to read API responses or config files, people checking one-line JSON from logs, anyone hunting for the mistake in a JSON file, and testers tidying sample data.
Does it cost anything?
No. No usage limits and no sign-up.
Is my JSON sent anywhere?
No. Formatting and checking happen on this page, so JSON with API keys or personal data never leaves your device.
How are errors shown?
You see the spot, like “line 3, column 5”, and what’s wrong (a missing comma, single quotes instead of double quotes, and so on). “Select the spot” selects that character on the left.
What if full-width or look-alike characters slip in?
Full-width colons, commas and spaces, and curly quotes like “ ”, aren’t allowed in JSON. You’re told which character it is (for example U+FF1A) and the plain character to use instead.
Can big numbers change?
No. The browser’s standard JSON reader rounds very large integers (about 16 digits and up), but this tool keeps every number exactly as written, so long IDs and decimals like 1.10 stay the same.
Can I read \u3042-style characters?
Tick “Show \u3042-style escapes as readable characters” and the result and tree show them as normal letters. Characters that JSON requires to be escaped, like line breaks and quotes, stay escaped, so the result is still valid JSON.
What is the tree view?
Switch the result to “Tree” to open and close objects and arrays as you explore. Handy for deeply nested JSON. There are “Expand all” and “Collapse all” buttons too.
What happens with duplicate keys?
In JSON, which value wins depends on the program reading it. This tool tells you the line of each repeated key and keeps both in the result.
Can it fix comments, trailing commas and single quotes?
Tick “Repair” and comments and trailing commas are removed and single-quoted strings become double-quoted. You’re told what was fixed and how many times. The result is valid JSON.
What does “one line” do?
It removes all spaces and line breaks for the smallest JSON, to save bandwidth or file size.
How do I use sort keys?
Sort two JSON files before comparing them to make differences easy to spot. Only object keys are sorted; array order is kept.
Can it open big files?
Yes. Everything runs on your device, so the limit is your device’s memory. In our tests a 3 MB JSON is formatted in under 3 seconds.
Does it work on a phone?
Yes. You can paste and copy the result.
Premium
One Premium. Every upgrade, as much as you like.
- All paid features in every extension
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- Extensions we release later are included
- Up to 3 browsers per person (home, work, phone)
- Monthly¥980/month
- Yearly¥9,800/year (about ¥817/month)
- Lifetime¥14,800 once
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