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Hazuu Tools

JSON Validator

Validate your JSON syntax instantly and pinpoint errors with line and column numbers.

JSON Input
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About JSON Validator

JSON Validator is a free online tool that checks whether a block of text is syntactically valid JSON according to RFC 8259. Paste your JSON data and click Validate to get an immediate pass or fail verdict. When the JSON is invalid, the tool reports the exact line and column number where parsing broke, so you can jump straight to the problem instead of scanning hundreds of lines manually.

Use this tool when a REST API call returns an unexpected 400, when a config file fails to load, or when you suspect a copy-paste error introduced a trailing comma or an unquoted key. JSON Validator focuses solely on correctness — it tells you whether the structure parses cleanly. If you already know the JSON is valid and just want it pretty-printed, the companion JSON Formatter tool handles indentation and sorting. If you need to shrink output for production, JSON Minifier handles that. This tool answers the single question: is it valid JSON at all?

All validation runs entirely in your browser using the native JSON.parse API. Your data is never uploaded, logged, or sent to any server, so API responses containing authentication tokens, database records, or other sensitive fields stay private on your own machine. There are no file-size limits, no rate limits, no accounts required, and no cost.

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Key Features

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Line and column error location

When JSON is invalid, the tool pinpoints the exact line and column of the first syntax error, eliminating the need to scan large documents by eye.

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Validate and format in one step

Click Format to both check syntax and auto-indent valid JSON with 2-space indentation, producing a readable version ready to copy.

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100% client-side via JSON.parse

Validation uses the browser's native JSON.parse function. Nothing leaves your machine, making the tool safe for API keys, tokens, and confidential payloads.

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Catches the full range of JSON syntax errors

Missing commas between key-value pairs, trailing commas in arrays and objects, single-quoted strings, unquoted keys, and invalid literal values like undefined are all detected.

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File upload support

Upload a .json or .txt file directly from disk when pasting a large document is inconvenient. The file is read locally and never transmitted.

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Sample fixtures for quick testing

Load a pre-built valid or invalid JSON sample with one click to verify the tool is working or to see what a specific error message looks like.

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How to Use

01

Paste Your JSON

Copy your JSON data and paste it into the editor, or upload a .json file.

02

Validate

Click "Validate" to check syntax. Errors are shown with line and column numbers.

03

Fix & Format

Fix any errors, then click "Format" to auto-indent your valid JSON for readability.

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Example

A missing comma after the "email" field causes a SyntaxError. The validator reports the exact line and column so you can fix it immediately.

Invalid JSON input
{
  "name": "Jane Smith",
  "age": 28,
  "email": "jane@example.com"
  "isActive": true
}
Validation result
Invalid JSON — Line 5, Column 3
Unexpected string in JSON at position 58

Fix: add a comma after the "email" line:
  "email": "jane@example.com",
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Common Use Cases

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    Debugging API responses and request bodies

    When a REST or GraphQL call returns a 400 or the client SDK throws a parse error, paste the raw response or request body here to confirm whether the payload is valid JSON before looking for application-level bugs.

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    Validating configuration files before deployment

    package.json, tsconfig.json, .eslintrc.json, and similar config files must be syntactically valid before any build tool reads them. Run a quick check here after editing them manually to catch stray commas or missing braces before they break a CI pipeline.

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    Checking generated or serialised output

    Code that builds JSON by string concatenation or templating is prone to producing malformed output. Paste a sample here to confirm the serialisation is correct, especially after adding new fields or changing data types.

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    Verifying pasted or imported data

    JSON copied from a browser console, a log file, or a third-party export often picks up stray characters. Validate it here to confirm it is clean before feeding it into a script or another tool.

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    Learning which syntax rules JSON enforces

    Unlike JavaScript object literals, JSON requires double-quoted keys, forbids trailing commas, and rejects undefined and NaN. Use the invalid sample fixture to see exactly how these rules are enforced and what error messages look like.

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Frequently Asked Questions

What is a JSON Validator? expand_more
A JSON Validator checks whether a string of text is valid JSON according to the JSON specification (RFC 8259). It identifies syntax errors like missing commas, unmatched brackets, trailing commas, and invalid values, and reports the exact location of each error.
What common JSON errors does this catch? expand_more
The validator catches missing or extra commas, unmatched braces or brackets, single quotes instead of double quotes, trailing commas in arrays or objects, unquoted keys, and invalid values like undefined or NaN.
Is my JSON data secure? expand_more
Yes. All validation runs entirely in your browser using native JSON.parse. Your data never leaves your machine and is not sent to any external server.
Can this tool also format my JSON? expand_more
Yes. Click the "Format" button to both validate and auto-format your JSON with consistent 2-space indentation, making it easier to read and debug.
How is JSON Validator different from JSON Formatter? expand_more
JSON Validator answers whether your JSON is syntactically correct and tells you exactly where an error is. JSON Formatter assumes the JSON is already valid and focuses on sorting keys, choosing indentation depth, or collapsing nodes. If you are unsure whether the JSON parses at all, start with the Validator; once you know it is valid, use the Formatter to adjust how it looks.
Why does JSON require double quotes but JavaScript does not? expand_more
JSON is a strict data-interchange format specified by RFC 8259, not a JavaScript syntax. It mandates double-quoted strings and disallows trailing commas, comments, and JavaScript-only values like undefined or NaN. JavaScript object literal syntax is more permissive, which is why JSON copied from a JS file often fails to validate.
What does the line and column number in the error mean? expand_more
The validator calculates the line and column by counting newlines in the input up to the position where JSON.parse failed. Line 1 is the first line of your input, and the column is the character position within that line. Jump straight to that location in your editor to find the syntax error.
Is there a file size limit? expand_more
There is no fixed limit. Because everything runs locally in your browser, you can validate large files — performance depends only on your device. For very large documents the Format step may take a moment to re-serialise the parsed result.