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JSON Linter - Online JSON Validator & Syntax Checker

Free online JSON linter and validator. Check JSON syntax, validate API payloads, and debug configuration files. 100% client-side - your JSON never leaves your browser.

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About This Linter

This linter validates JSON syntax and structure using the native browser JSON.parse. It attempts to surface multiple syntax errors by re-running the parser after masking earlier issues. All processing happens entirely in your browser - no data is sent to any server.

What is a JSON Linter?
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A JSON linter is a tool that checks your JSON data for syntax errors, structural problems, and common formatting issues before that JSON is consumed by applications or APIs. A single misplaced comma, missing quote, or extra brace can break an entire integration.

Why Use This JSON Linter?
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FeatureDescription
100% Client-SideYour JSON never leaves the browser
Fast FeedbackErrors highlighted with line-level context
Formatted PreviewSee pretty-printed version of your JSON
Multiple ErrorsSurfaces several issues in one pass
Safe for Sensitive DataNo backend storage or logging

Common JSON Syntax Errors
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Missing or Extra Commas
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The most frequent JSON error is incorrect comma placement:

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// Wrong - trailing comma
{
  "name": "app",
  "version": "1.0",  // <-- trailing comma not allowed
}

// Wrong - missing comma
{
  "name": "app"
  "version": "1.0"  // <-- missing comma
}

// Correct
{
  "name": "app",
  "version": "1.0"
}

Unquoted Keys or Single Quotes
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JSON requires double quotes for all strings:

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// Wrong - unquoted key
{
  name: "app"
}

// Wrong - single quotes
{
  'name': 'app'
}

// Correct
{
  "name": "app"
}

Incorrect Data Types
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// Wrong - undefined is not valid JSON
{
  "value": undefined
}

// Wrong - NaN is not valid JSON
{
  "value": NaN
}

// Correct - use null for missing values
{
  "value": null
}

Typical Use Cases
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API Payloads
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Validate REST API request and response bodies:

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{
  "userId": 123,
  "action": "update",
  "data": {
    "email": "user@example.com",
    "preferences": {
      "notifications": true,
      "theme": "dark"
    }
  }
}

Configuration Files
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Lint package.json, tsconfig.json, and other config files:

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{
  "name": "my-project",
  "version": "1.0.0",
  "scripts": {
    "build": "tsc",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.18.0"
  }
}

CI/CD Settings
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Validate GitHub Actions JSON expressions, AWS CloudFormation, and more:

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{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyBucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "BucketName": "my-bucket"
      }
    }
  }
}

Database Documents
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Lint MongoDB documents, Elasticsearch queries, and NoSQL data:

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{
  "_id": "doc123",
  "type": "user",
  "profile": {
    "name": "John Doe",
    "tags": ["admin", "developer"]
  },
  "createdAt": "2024-01-15T10:30:00Z"
}

JSON vs JavaScript Objects
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JSON is not the same as JavaScript objects. Key differences:

FeatureJSONJavaScript
KeysMust be double-quotedCan be unquoted
StringsDouble quotes onlySingle or double quotes
CommentsNot allowedAllowed
Trailing commasNot allowedAllowed (ES5+)
FunctionsNot allowedAllowed
Pro Tip
If you’re pasting JavaScript object literals, make sure to convert them to valid JSON first by double-quoting keys and removing trailing commas.

Privacy & Security
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All processing happens directly in your browser:

  • No Server Communication: Your JSON data never leaves your device
  • No Storage: Nothing is saved to localStorage, cookies, or servers
  • Open Source: All code is transparent and auditable

Related Tools#

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