JSON Validator Online — Check JSON Syntax Instantly
Validate your JSON data with real-time syntax checking. Get plain-English error explanations with exact line and column numbers. Free, no sign-up.
JSON Input
About JSON Validator
Is your JSON valid? Paste it here and find out instantly. AllJSONTools' JSON Validator checks your data against the JSON specification (RFC 8259) in real time, pinpointing the exact line and column of every syntax error. Unlike basic validators that just say "invalid", this tool explains what went wrong in plain English — and if you need to fix it, one click takes you to our AI-powered JSON fixer. Whether you are debugging an API response, checking a config file before deployment, or validating data before importing it into a database, this validator gives you clear, actionable feedback. No sign-up, no server uploads — everything runs in your browser.
How to Use JSON Validator
Paste or Upload JSON
Paste JSON into the editor, drag and drop a .json file, or use the upload button. The validator auto-detects paste and validates immediately — no button click needed.
Review the Result
Valid JSON shows a green checkmark with structure stats (key count, depth, size). Invalid JSON shows the exact error location, a plain-English explanation, and suggestions for how to fix it.
Fix or Continue
If your JSON is invalid, click "Fix Automatically with AI" to repair it instantly. If it is valid, use the quick actions to format it, view it as a tree, or convert it to TypeScript.
Common JSON Errors & How to Fix Them
These are the most frequent JSON syntax mistakes. Our tool detects all of them.
Trailing Comma
JSON does not allow trailing commas after the last property.
{ "name": "John", "age": 30, }{ "name": "John", "age": 30 }Single Quotes
JSON requires double quotes for all strings and keys.
{ 'name': 'John' }{ "name": "John" }Unquoted Keys
All keys must be wrapped in double quotes.
{ name: "John" }{ "name": "John" }Comments
Standard JSON does not support comments.
{ "a": 1 // comment }{ "a": 1 }undefined / NaN
Use null instead of undefined. NaN is also not valid JSON.
{ "value": undefined }{ "value": null }Missing Brackets
Every opening bracket must have a matching closing bracket.
{ "items": [1, 2, 3{ "items": [1, 2, 3] }For a comprehensive guide, read our article on fixing common JSON errors.
Common Use Cases
Validate API Responses
Paste API responses to verify they are valid JSON before processing them in your application. Catch malformed responses from third-party APIs before they cause runtime errors.
Check Config Files
Validate package.json, tsconfig.json, .eslintrc.json and other config files before committing. Catch trailing commas, missing quotes, and bracket mismatches early.
Pre-Import Validation
Verify JSON data integrity before importing into databases, message queues, or data pipelines. Prevent bad data from entering your system.
Debug JSON.parse() Errors
When your code throws "SyntaxError: Unexpected token", paste the JSON here to see exactly where the error is and what caused it.
Validate Webhook Payloads
Check incoming webhook data from Stripe, GitHub, Slack and other services. Ensure the payload is valid before processing it in your handler.
CI/CD Pipeline Checks
Validate JSON artifacts, build configs, and deployment manifests as part of your development workflow.
Why Use Our JSON Validator?
Instant Validation
Results appear the moment you paste, with no page reload or button click required
Plain-English Errors
Every error is explained in human language, not just "Unexpected token at position 42"
Exact Error Location
Line and column numbers with editor highlighting so you can jump straight to the problem
AI Fix Integration
One click takes invalid JSON to our AI fixer, which repairs it automatically
Structure Stats
Valid JSON shows key count, nesting depth, and file size at a glance
100% Client-Side
Your data never leaves your browser. Safe for API keys, tokens, and production configs
Key Features
Real-time validation on paste — no button click needed
Exact error location with line and column numbers
Plain-English error explanations for every syntax issue
Monaco editor with syntax highlighting and bracket matching
One-click AI fix for invalid JSON
Structure stats for valid JSON (keys, depth, size, type)
Drag and drop .json file upload
Share validation results via URL
Works fully offline as a Progressive Web App
Keyboard shortcut: Cmd+Enter to validate
100% Client-Side Processing
Your data never leaves your browser
All processing happens in your browser using JavaScript. Your data is never sent to our servers or any third party. Safe for sensitive data, API keys, and production configs.
Frequently Asked Questions
Quick answers to common questions about json validator
JSON validation checks whether a string conforms to the JSON specification (RFC 8259). This means all keys are double-quoted, strings use double quotes, there are no trailing commas, no comments, and all brackets and braces are properly matched. Our validator checks all of these rules instantly.
JSON validation checks if the syntax is correct (is it valid JSON?). JSON Schema validation checks if the structure and data types match a predefined schema (does it have the right fields?). Use this tool for syntax validation. Use our JSON Schema Validator for schema validation.
The most common reasons are: trailing commas after the last property, single quotes instead of double quotes, unquoted keys, JavaScript comments (// or /* */), undefined or NaN values, and missing or mismatched brackets. Our validator explains the exact cause for your specific error.
Yes. The validator uses the Monaco editor (same engine as VS Code) and handles files up to 10 MB efficiently. All processing happens in your browser — there is no upload delay.
Yes. All validation runs 100% client-side in your browser using JavaScript. Your JSON data is never uploaded to any server, never logged, and never stored. Safe for API keys, tokens, and production data.
The validator shows the exact line and column of the error, explains what went wrong in plain English, and suggests how to fix it. You can also click "Fix Automatically with AI" to repair the JSON instantly using our AI-powered fixer.
No, this tool validates JSON syntax only. For JSON Schema validation (checking if data matches a schema definition), use our dedicated JSON Schema Validator tool.
This validator checks standard JSON (one value per document). JSONL is a format where each line is a separate JSON value. To validate JSONL, validate each line individually.
Learn More
{ }
Fix Common JSON Errors
A comprehensive guide to the 9 most frequent JSON syntax mistakes and how to fix them.
< / >
How to Parse JSON in JavaScript
Learn JSON.parse(), JSON.stringify(), error handling, and best practices.
=> { }
JSON Schema Explained
What is JSON Schema, why use it, and how to write validation schemas.
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