JSON Validator

Check whether any JSON is valid in real time. Catch syntax errors, trailing commas, single quotes, and unquoted keys with the exact parser message and position. Free, private, and runs entirely in your browser — nothing is ever uploaded.

Paste your JSON

Real-time validation as you type
Waiting for input
Tip: Validation runs as you type using the browser's native JSON.parse — the same parser your code uses. Press Ctrl + Enter to validate and format instantly.

Validation result

Waiting for input
Waiting for input — paste JSON to begin.

Validation results will appear here. Paste JSON on the left and click Validate JSON.

What does a JSON Validator do?

A JSON validator checks whether a piece of text conforms to the JSON specification (RFC 8259). It parses the input using the exact same rules a browser or server would use, and reports whether the JSON is valid or exactly where it fails — down to the line and character position.

JSON is a strict format. Unlike JavaScript object literals, JSON doesn't allow trailing commas, single quotes, unquoted keys, comments, or non-ASCII characters like curly quotes pasted from Word or Google Docs. Any of these will cause a parser to reject the entire document.

This tool uses the browser's native JSON.parse function, so the validation result matches what your own code will see in production. Beyond validation, the tool can also format your JSON for readability, count keys, measure the file size, and calculate nesting depth — all without sending anything to a server.

How to validate JSON

  1. Paste your JSON — drop any JSON into the input area, from an API response, a config file, or a database export.
  2. Watch the validator badge — as you type, the badge above the input updates in real time. It tells you instantly whether the JSON is valid or invalid.
  3. Fix any errors — if the JSON is invalid, the exact parser message appears below the input with the character position of the problem. Fix it and the badge turns green.
  4. Review the stats — once valid, the tool shows key count, file size, and nesting depth.
  5. Format if needed — click Validate JSON to see a prettified version of the JSON on the right, which you can copy or download.

Why use this JSON Validator?

100% client-side

Your JSON never leaves your device. Everything runs in the browser using native JavaScript APIs. No server, no logs, no uploads.

Real-time validation

The validator checks your JSON as you type, using the same parser your browser uses. If it passes here, it parses in your code.

Exact error position

When JSON is invalid, the tool shows the browser's exact parser message including the character position — the same message you'd see in your console.

Key count and size

See exactly how many keys your JSON contains, how many bytes it uses, and how deeply it's nested. Useful for quick sanity checks.

Format for readability

The tool can pretty-print valid JSON with proper indentation, making it easier to read, review, and debug.

Works offline

Once the page loads, validation runs entirely on your device. No internet connection is needed after the initial page load.

Most common JSON errors (and how to fix them)

These are the mistakes that cause 90% of JSON parsing failures. All of them are caught by this validator, and all of them are easy to fix once you know what to look for.

ErrorInvalid exampleFix
Trailing comma{"a": 1, "b": 2,}Remove the comma after the last item: {"a": 1, "b": 2}
Single quotes{'name': 'John'}Use double quotes: {"name": "John"}
Unquoted keys{name: "John"}Quote the key: {"name": "John"}
Missing comma{"a": 1 "b": 2}Add the comma: {"a": 1, "b": 2}
Curly quotes{"name": "John"} (smart quotes)Replace with straight quotes
Comment in JSON{"a": 1 /* note */}Remove the comment — JSON doesn't support comments
undefined or NaN{"value": undefined}Use null instead: {"value": null}
Unescaped newline{"text": "line1
line2"}		Escape it: {"text": "line1\\nline2"}

The trailing comma is the single most common mistake — it's valid in JavaScript, Python, and many other languages, but JSON deliberately disallows it. Similarly, single quotes are legal in JavaScript but not JSON. This tool uses the browser's own parser, which follows the RFC 8259 spec strictly, so it catches every one of these.

JSON syntax validation vs. JSON Schema validation

These are two different layers of validation, and understanding the difference helps you know when to use which tool.

Syntax validation (what this tool does)

Syntax validation checks whether the text is well-formed JSON. It asks: does this follow the grammar rules of JSON? Are the braces balanced? Are the quotes correct? Is the comma placement valid? If syntax validation fails, nothing else can succeed — the parser can't even read the document.

Schema validation (a separate step)

Schema validation checks whether the structure of valid JSON matches an expected shape. It asks: does this object have all the required fields? Is the age field a number instead of a string? Does this array contain at least one item? JSON Schema is a separate specification that describes the shape of JSON documents, and it runs on top of syntax validation.

The two work together: syntax validation is the first gate, and schema validation is the second. This tool handles the first gate. If you need schema validation, tools like Ajv or jsonschemavalidator.net are the right choice once your JSON passes syntax validation.

JSON validation best practices

  • Validate early, not late. Check JSON at the boundary of your application — when it enters from an API, file, or user input — rather than deep in the processing pipeline.
  • Don't regex-repair JSON. Complex JSON shouldn't be fixed with regex substitutions. If the input is broken, find the actual cause. Regex repairs can silently corrupt data.
  • Combine with schema validation. Syntax validation ensures the document can be parsed. Schema validation ensures it matches your expected structure. Use both.
  • Keep raw and formatted copies. Store minified JSON for production and a prettified copy for debugging.
  • Validate in CI. Add a JSON validation step to your build pipeline so a broken config file fails fast, before it hits a server.

Frequently asked questions

A JSON validator checks whether a piece of text conforms to the JSON specification (RFC 8259). It parses the input using the same rules a browser or server would use, and reports whether the JSON is valid or exactly where it fails.
The most common errors are trailing commas after the last item in an array or object, single quotes instead of double quotes, unquoted object keys, missing commas between items, and non-ASCII characters such as curly quotes pasted from Word or Google Docs.
Yes. When the JSON is invalid, the tool reports the browser's exact parser message including the character position of the error. This is the same message you would see in your browser's developer console.
No. Everything runs in your browser using the native JSON.parse function. No data is sent to any server. You can even disconnect from the internet after the page loads and it will still work.
A validator tells you whether JSON is valid. A formatter takes valid JSON and reformats it with indentation for readability. This tool does both — it validates first, then can format the output.
No. This tool validates JSON syntax, which is the first step. JSON Schema validation checks whether the data matches a specific structure (types, required fields, constraints). Schema validation is a separate layer that runs after syntax validation passes.
Not as a single document. JSONL has one JSON object per line. Each line is valid JSON on its own — you would validate them individually.
Yes. Once the page loads, validation runs entirely on your device. No internet connection is needed after the initial page load.
Yes, completely free. No signup, no watermark, no limits. Validate as much JSON as you want.