API debugging
Make a one-line API response readable before you hunt for a field.
JSON Formatter and Validator
Make messy JSON readable and find syntax mistakes fast. Everything stays in your browser.
Your files stay with you. Your files never leave your browser. This tool runs on your device: nothing is uploaded to our servers, so there is nothing for us to store or see.
How to use it
- Paste your JSON or open a .json file.
- Pick the layout: 2 spaces, 4 spaces, tab or minified, and sort keys if you like.
- Copy or download the result. If there is a mistake, the error tells you the line and column.
Where it helps
Fixing config files
Find the stray comma that stops an app from starting.
Shrinking payloads
Minify JSON before storing it or putting it in a request.
Good to know
Stays in your browser
Your text is processed on your device and never sent to our servers.
Mind live secrets
Avoid pasting production keys or tokens on a shared computer.
Strict JSON only
Comments, single quotes and trailing commas are flagged.
Sort keys is optional
Leave it off to keep the original key order.
Questions people ask
How do you format and validate JSON, and find the line with the error?
Paste your JSON or open a .json file, then pick 2 spaces, 4 spaces, tab or minified, and sort the keys if you like. Valid JSON is re-indented at once. If it's invalid, the tool names the first problem with its line and column, such as a trailing comma or single quotes, and Go to line selects the spot.
- Line:col Error location. With Go to line.
- 4 Layouts. 2, 4, tab, minified.
- Exact Numbers and key order. Kept as written.
- ~5M Characters. Per paste.
How do I find the error in my JSON?
Paste it in. If the JSON is invalid, the tool names the first problem with its line and column, such as a trailing comma, single quotes instead of double quotes or a missing comma, and the Go to line button selects the exact spot. Fix it, and the formatted result appears straight away.
Does it change my numbers or the order of keys?
No. The formatter only changes spaces and line breaks, so large numbers such as 12345678901234567890 and the order of your keys stay exactly as you wrote them. Many online formatters quietly round long numbers. Only the optional Sort keys switch reorders anything, and only when you turn it on.
Why is JSON with comments or single quotes rejected?
Strict JSON doesn't allow comments, single quotes, trailing commas or unquoted key names. Those belong to JavaScript objects or JSON5. APIs and most parsers expect strict JSON, so the tool flags them. Remove the comments and switch to double quotes, and the formatter will accept the text.
Is my data uploaded?
No. Your text is processed in your browser and never reaches our servers, so it's safe to paste API responses and internal data. As a general habit, avoid pasting live passwords, keys or tokens on a shared or public computer, whatever tool you use, because they may linger in the clipboard.
How big a file can I format?
Up to about 5 million characters. Beyond that a browser tab can slow down or run out of memory, so the tool asks for a smaller sample. For very large files, format a slice that contains the part you're investigating, or use a command-line tool such as jq on your own machine.
What does minified JSON mean?
Minified JSON has every unneeded space and line break removed, so it fits on one line and takes fewer bytes. It's what APIs usually send and what you'd store in a database column. Choose Minified as the layout, then copy or download the result for your request body or file.
Should I use 2 spaces, 4 spaces or tabs?
Any of them is valid JSON. Two spaces is the most common choice in web projects and keeps deep nesting readable. Four spaces matches many Python and Java style guides. Tabs let each reader set their own width. Match whatever the rest of your project already uses.
What does Sort keys do?
It orders the keys inside every object alphabetically, at every level. That makes two versions of the same data easier to compare, line by line, in a diff tool. Leave it off when key order matters to people reading the file, or when you need the output to match the original.
Can I open a .json file from my computer?
Yes. Use the file button to open a .json file and it loads straight into the editor. Nothing is uploaded: the browser reads the file locally. When you're done, download the formatted version with a click, or copy it to the clipboard for pasting elsewhere.
Why does my API response show as one long line?
APIs send minified JSON to save bandwidth, so it arrives without line breaks. Paste it here and choose two or four spaces to make it readable. Then you can follow the nesting, spot the field you need and check the values the API actually returned.
What are the most common JSON mistakes?
A trailing comma after the last item, single quotes around strings or keys, a missing comma between items, unquoted key names and comments. Copying a JavaScript object and expecting it to be JSON causes most of these. The error message here names the exact problem and its position.
Is JSON the same as a JavaScript object?
No. JSON is a text format that borrows JavaScript's syntax but is stricter. Keys must be in double quotes, strings use double quotes, and functions, comments, undefined and trailing commas aren't allowed. Valid JSON is always a valid JavaScript value, but not the other way round.
Can I convert JSON to other formats?
Yes, with the related tools. JSON to CSV turns a list of records into a spreadsheet file for Excel or Google Sheets. JSON to YAML makes config files for tools such as Kubernetes and CI pipelines. Format and check the JSON here first, so the conversion starts from valid input.
Does it work on a phone?
Yes. You can paste JSON and read the formatted result on a phone, which helps when checking an API response or a webhook payload away from your desk. Long, deeply nested files are easier to work through on a larger screen, but everything still runs locally on your phone.
Is the JSON formatter free?
Yes. It's free with no sign-up, no limit on use and no data sent to a server. It's one of the free developer tools from Marketiism, which also builds business software. That platform's API and webhooks send JSON, so this tool is handy when you connect it.
Want this inside your own account?
Marketiism keeps your invoice numbers, GST reports, UPI payment links and WhatsApp reminders in one place. Leave your details and we'll call to set it up for your business, or start the trial yourself.
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