JSON Validator Online — Syntax Checker & Linter

Validate JSON online with VS Code-style squiggle error highlighting. Shows ALL syntax errors at once with exact line and column. One-click Fix All for missing commas, unquoted keys. Free JSON syntax checker.

What is ilovejson?

ilovejson is a free, fast, and fully private online JSON tool built for developers. It runs entirely in your browser — pasted and opened JSON is processed locally. Open URL contacts the address you provide, and Share creates a link containing your data; only share data you intend recipients to see.

Unlike most JSON formatters that stop at the first syntax error, ilovejson shows all errors at once with red wavy underlines, exact line and column numbers, and one-click Fix All — just like VS Code.

How to Format JSON Online

Paste JSON into the editor or choose Open file.
Choose Tree to explore nested objects, or keep Text to edit your JSON.
Click Format (or press Ctrl+Shift+F) to pretty-print the JSON back into the editor.
Switch to Text view to see the formatted output. Use Wrap, Unwrap, or Minify to control the output style.
Copy or download your formatted JSON.

Common JSON Errors and How to Fix Them

Missing comma: Every property in a JSON object must be separated by a comma. ilovejson highlights the exact value missing the comma and offers a Fix All button to insert all missing commas at once.
Trailing comma: Standard JSON does not allow a comma after the last item in an object or array. JSON5 does allow this — paste your JSON5 into ilovejson and it will be converted automatically.
Unquoted keys: JSON requires all object keys to be double-quoted strings. JavaScript object literals and Python dicts often have unquoted keys — ilovejson detects and fixes these automatically.
Single-quoted strings: JSON only allows double quotes. Single-quoted strings (common in Python and JavaScript) are detected and converted automatically.
Bad control character: Invisible control characters (like tabs or newlines inside string values) cause JSON parse failures. These are highlighted and can be found using the search feature.

Frequently Asked Questions

Is my JSON data private?

JSON formatting and validation run locally in your browser. Open URL sends a request to the supplied URL. Shared links contain the JSON in the URL, so avoid sharing secrets. The site also loads Firebase Analytics for usage measurement.

What formats does ilovejson support?

Standard JSON, JSON5 (with // comments and trailing commas), JSONL/ndjson (JSON Lines), Python dicts (None/True/False), Ruby Hashes (symbol => syntax), PHP arrays, and JavaScript object literals with unquoted keys — all auto-detected.

How do I compare two JSON files?

Click the Diff button in the top bar. The editor switches to a side-by-side view — paste your original JSON on the left and modified JSON on the right. Added lines are highlighted green, removed lines red, and changed lines yellow.

What is JSONL (JSON Lines)?

JSONL (also called ndjson or newline-delimited JSON) is a format where each line is a valid JSON object. It is commonly used for log files, data pipelines, and streaming APIs. ilovejson parses each line separately and shows them as individual collapsible records in the tree view.

Can ilovejson handle large JSON files?

Yes. The tree view uses virtual scroll — only the rows visible on screen are rendered as DOM nodes, regardless of file size. Practical file limits depend on your browser, available memory, and the structure of the data.

What is JSON5?

JSON5 is a superset of JSON that allows JavaScript-style comments (// and /* */), trailing commas, unquoted keys, and single-quoted strings. It is often used in configuration files (like VS Code's settings.json). ilovejson converts JSON5 to standard JSON automatically.

How do I load JSON from a URL?

Click Open URL in the top bar and paste any URL that returns JSON. Alternatively, add ?url=https://api.example.com/data to the ilovejson URL to load it directly on page open — useful for sharing pre-loaded views.