Is the JSON Validator free to use?

Yes, completely free. No signup, no account, no payment required. DevToolsHub is a collection of free developer tools funded by optional ads — your workflow is never paywalled.

Does it store or send my data anywhere?

No. All validation happens entirely in your browser using JavaScript. Your JSON input is never uploaded to a server, stored in a database, or logged anywhere. What you paste stays on your device.

What JSON standard does this validator follow?

It follows RFC 8259, the official JSON specification published by the IETF. The validator uses your browser's native JSON.parse() function, which is the most standards-compliant parser available. Any input that passes this validator will be accepted by any RFC 8259-compliant parser.

Does it support JSON5 or JSONC (JSON with Comments)?

No. This validator checks standard JSON only. JSON5 and JSONC are separate formats that relax certain rules (allowing comments, trailing commas, single quotes, etc.). If you need to validate those formats, look for a dedicated JSON5 or JSONC validator. Note that many code editors (like VS Code) use JSONC for their settings files, which is why comments may work there but fail here.

What's the maximum file size I can validate?

There is no hard limit imposed by the tool. However, since validation runs in your browser, extremely large inputs (tens of megabytes) may cause the editor to feel sluggish or trigger browser memory limits. For most practical use cases — config files, API payloads, data fixtures — performance is instant.

Why does my JSON fail here but work in JavaScript code?

JavaScript object literals are more permissive than JSON. JavaScript allows single quotes, unquoted property names, trailing commas, comments, and values like undefined and NaN. Standard JSON (RFC 8259) does not allow any of these. If your JSON works in a .js file but fails here, it's likely using one of these JavaScript-only extensions. Convert single quotes to double quotes, remove trailing commas, quote all property names, and remove comments.

Can it find all errors at once?

Currently, the validator reports the first error it encounters, because JSON.parse stops at the first syntax error. This is a limitation of the native parser. In practice, fixing the first error often resolves cascading errors — and once you fix it, the validator re-runs automatically and will surface the next error if one exists. A multi-error parser may be added in a future update.

Does it work on mobile devices?

Yes. The JSON Validator is fully responsive and works on phones, tablets, and desktops. The code editor adapts to smaller screens, and all buttons are sized for touch interaction. Dark mode is supported and follows your system or browser preference.

🛠️DevToolsHub

JSON Validator

Validate JSON syntax and find errors with line numbers.

What is JSON Validator?

A JSON Validator is a tool that checks whether a JSON (JavaScript Object Notation) string conforms to the official JSON syntax specification. It parses your input and reports any syntax errors it finds — complete with line numbers, column positions, and human-readable error messages so you can fix problems quickly.

JSON is the de facto standard for data interchange on the web. It's used in REST APIs, configuration files, NoSQL databases (like MongoDB), package manifests (package.json), and countless other contexts. Even a single misplaced comma or missing quote can render an entire JSON document unparseable, causing applications to crash or fail silently. A validator catches these issues before they reach production.

The most common JSON errors include trailing commas (a comma before a closing } or ]), single quotes instead of the required double quotes, missing brackets or braces, unquoted property names, and comments (which are not allowed in standard JSON, even though many developers add them out of habit). JavaScript objects allow all of these, which is why JSON that works in a .js file can fail when parsed as strict JSON.

Unlike a JSON Formatter, which reformats and pretty-prints valid JSON, a validator focuses on correctness. It tells you whether the JSON is valid and, if not, exactly where and whyit's broken. You can use a validator to check API responses, debug configuration files, verify data payloads before sending them to a server, or troubleshoot parsing errors in your code. Once your JSON is valid, you can feed it into a formatter for readability.

How to Use JSON Validator

Paste or type your JSONinto the input editor above. You can also click "Load Valid Example" or "Load Invalid Example" to see how the tool behaves with different inputs.
The validator runs automaticallyas you type (after a short 300 ms debounce). You can also click the "Validate" button to force an immediate check.
If your JSON is valid, you'll see a green "Valid JSON ✓" badge along with statistics: top-level type, size, key/item count, and maximum nesting depth.
If your JSON is invalid, you'll see a red "Invalid JSON ✗" badge and a detailed error list showing the error message, line number, and column position.
Use the error details to fix the problem in the editor. The validator will re-run automatically and update the result.
Click Copy Input to copy your JSON to the clipboard, or Clear to start over.

Common JSON Errors

Trailing Commas

JSON does not allow a comma after the last element in an object or array. For example, {"a":1,} is invalid — remove the trailing comma to fix it. This is the most common JSON error, especially when hand-editing files.

Single Quotes Instead of Double Quotes

JSON requires double quotes (") for all strings and property names. Single quotes (') are not valid. {'name':'test'} must be rewritten as {"name":"test"}.

Missing Brackets and Braces

Every opening { must have a matching closing }, and every opening [ must have a matching closing ]. Mismatched or missing brackets cause "Unexpected end of JSON input" or "Unexpected token" errors.

Unquoted Property Names

In JavaScript objects, you can write {name:"test"}. In JSON, property names must always be in double quotes: {"name":"test"}.

Comments

Standard JSON (RFC 8259) does not support comments. Neither // line comments nor /* block comments */ are allowed. If you need comments in your JSON files, consider using JSONC (JSON with Comments) or JSON5, but be aware that standard JSON parsers will reject them.

Extra Characters After Valid JSON

JSON.parse expects the entire input to be a single JSON value. Any non-whitespace content after the closing bracket or final value will trigger an error. For example, {"a":1} extra is invalid because of the trailing extra.

Features

Real-time validation— errors are reported automatically as you type, with a 300 ms debounce to avoid flicker.
Precise error locations — each error includes the line number, column, and character position so you can jump straight to the problem.
Detailed error messages — human-readable descriptions of what went wrong, not cryptic parser codes.
JSON statistics — for valid input, see the top-level type (object, array, string, number, boolean, null), size in bytes, key or item count, and maximum nesting depth.
Example loader — one-click buttons to load a valid and an invalid example, so you can see both states instantly.
Syntax highlighting — the input editor uses CodeMirror with JSON language support and dark mode integration.
100% client-side — all validation happens in your browser. Your data never leaves your device.
RFC 8259 compliant — uses the native JSON.parse implementation, which follows the official JSON specification.
Responsive design — works on mobile, tablet, and desktop with full dark mode support.

Frequently Asked Questions