About JSON Lint
This JSON lint tool finds syntax errors in your JSON, reports the line and column of the first one, and can repair the most common mistakes for you with Auto-fix. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
Linting JSON mostly means catching things that look fine in a JavaScript file but are not valid JSON: single-quoted strings, keys without quotes, comments and trailing commas. A config pasted from code, such as {name: 'Ada', "tags": ["a","b",],}, fails at line 1, column 2, with Unexpected character 'n', expected a quoted key. Press Auto-fix and it becomes {"name": "Ada", "tags": ["a","b"]}.
The Auto-fix button appears only when the repaired text is itself valid. If it does not appear, the problem is something the tool cannot guess, such as a missing bracket or a missing value. Fix that by hand using the line and column, and the lint runs again as you type.
Other messages you may see: Unterminated string for a missing closing quote, Control character in string for a real line break inside a string, Invalid escape sequence for a backslash followed by an unsupported letter, and Nesting too deep for documents nested more than 512 levels.
How to use JSON Lint
- Paste your JSON into the box. The tool checks it as you type and shows Valid JSON or the error.
- Choose a tab: Format to pretty-print, Minify to remove whitespace, Validate to check only, Sort keys to order the keys, Tree to browse, Escape to make or read a JSON string, or To CSV for a table.
- For Format and Sort keys, choose the indent: 2 spaces, 4 spaces or Tab.
- If you see Invalid JSON at line and column, go to that position. For a common mistake, press Auto-fix and check the result.
- In Tree, open and close branches, and click a key to copy its JSON path, such as $.users[0].name.
- Use Copy to take the output, or Download to save it as a .json file (a .csv file for To CSV).
Features
- Pretty-print with 2 spaces, 4 spaces or tabs.
- Minify to a single line with no extra whitespace.
- Validation that reports the line, the column and a plain-English message for the first error.
- Auto-fix for single quotes, unquoted keys, trailing commas and comments. The button only appears when the repaired text is valid.
- Tree view with collapsible branches, item counts and one-click copy of the JSON path of any key.
- Sort keys alphabetically at every level, without changing array order.
- Escape and unescape a JSON string. Unescape reads Unicode escapes, including emoji pairs.
- JSON to CSV for an array of objects, with the union of all keys as the header.
- Copy and Download of the result.
- All processing happens in your browser tab, with no server round trip.
Worked examples
{name: 'Ada', "tags": ["a","b",],} gives Invalid JSON at line 1, column 2: Unexpected character 'n', expected a quoted key
After Auto-fix: {"name": "Ada", "tags": ["a","b"]}
{"a": "x\y"} gives Invalid JSON at line 1, column 8: Invalid escape sequence
\y is not a valid JSON escape. The valid ones are \" \\ \/ \b \f \n \r \t and \uXXXX.
{"a": 01} gives Invalid JSON at line 1, column 8: Unexpected character '1', expected ',' or '}'
Numbers cannot have a leading zero.
Privacy: how it works
- Your JSON is processed by code in your browser tab. Nothing is sent to Ulkaa or to any other server, which you can confirm in the Network tab of your browser developer tools.
- API responses, config files and database exports often contain tokens, emails and personal data, so a formatter that does not upload them is the safe kind to paste into.
Tips
- Fix the first error only, then look again. Later errors often vanish, because one missing quote can make everything after it look wrong.
- Sort the keys of two JSON files with the same settings before you compare them. A text diff then shows only the real differences.
- Use the Tree view to find a path, then copy it. That is quicker than counting brackets in a long response.
- To put text with quotes and line breaks into a JSON field, paste it in Escape and copy the result between the quotation marks.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial and no credit card. Ulkaa Tool does the work with your own device, so there is no server bill to pass on to you.
Do I need an account?
No. There is no sign-up and no login. Open the page and use it. An Ulkaa account is not needed for anything on this tool.
Does it run in my browser?
Yes. Your JSON are processed by code running in your browser tab, on your own device.
Is my data uploaded?
No. Your JSON are never sent to Ulkaa or to anyone else. You can check this yourself by watching the Network tab in your browser developer tools while you use the tool.
What does JSON lint check?
Syntax only: whether the text is valid JSON. It does not enforce a style guide or a schema.
What does Auto-fix change?
It converts single quotes to double quotes, adds quotes to bare keys, removes // and /* */ comments and removes trailing commas. It does so only if the result is valid.
Why does my line number look wrong?
The position is where the parser noticed the problem. A missing quote or bracket is often reported a little after the real mistake, so check the lines just above it.
More JSON Formatter and Validator pages
- JSON Formatter and ValidatorFormat, minify and validate JSON, find errors by line and column, browse it as a tree, and fix common mistakes in one click.
- JSON ValidatorCheck that your JSON is valid and find the first error by line and column.
- JSON MinifierRemove the extra whitespace from JSON to make it smaller.
- JSON BeautifierPretty-print JSON so it is easy to read.
- JSON ViewerExplore JSON as a collapsible tree and copy the path of any value.
- JSON Escape and UnescapeEscape quotes, backslashes and line breaks for JSON, or turn an escaped string back into plain text.
- JSON Key SorterSort the keys of every object in your JSON alphabetically.
- JSON to CSV ConverterTurn a JSON array of objects into a CSV table you can open in a spreadsheet.