10 JSON Debugging Tips Every Developer Should Know

1. Use a JSON Validator First

Before diving into complex debugging, always run your JSON through a validator. This simple step catches 90% of common syntax errors instantly.

Why this matters:

• Identifies exact line and column numbers of errors
• Provides specific error messages (not generic "parse error")
• Catches multiple errors in one pass
• Saves hours of manual inspection

Use our free JSON validator to get instant error detection with helpful suggestions.

2. Format Your JSON for Better Visibility

Minified or poorly formatted JSON is nearly impossible to debug. Always format your JSON with proper indentation before attempting to fix issues.

// ❌ Hard to debug
{"users":[{"id":1,"name":"Alice","settings":{"theme":"dark","notifications":true}},{"id":2,"name":"Bob"}]}

// ✅ Easy to debug
{
  "users": [
    {
      "id": 1,
      "name": "Alice",
      "settings": {
        "theme": "dark",
        "notifications": true
      }
    },
    {
      "id": 2,
      "name": "Bob"
    }
  ]
}

Use a JSON formatter to instantly beautify minified JSON and spot structural issues.

3. Check for Trailing Commas

Trailing commas are one of the most common JSON errors, especially for developers coming from JavaScript where they're allowed.

// ❌ Invalid - trailing comma after last property
{
  "name": "John",
  "age": 30,
  "city": "New York",  // ← This comma is invalid
}

// ❌ Invalid - trailing comma in array
{
  "skills": ["JavaScript", "Python", "SQL",]  // ← Invalid
}

// ✅ Valid - no trailing commas
{
  "name": "John",
  "age": 30,
  "city": "New York"
}

{
  "skills": ["JavaScript", "Python", "SQL"]
}

Quick fix: Search for },, or ],[ followed by a closing bracket or brace.

4. Verify Quote Types

JSON requires double quotes for all strings. Single quotes will cause parse errors.

// ❌ Invalid - single quotes
{
  'name': 'John',
  'email': 'john@example.com'
}

// ✅ Valid - double quotes
{
  "name": "John",
  "email": "john@example.com"
}

Common sources of this error:

• Copying from JavaScript code that uses single quotes
• Manual typing without syntax highlighting
• Pasting from text editors that auto-convert quotes

5. Validate Escape Sequences

Special characters in strings must be properly escaped. Common issues include unescaped quotes, backslashes, and control characters.

// ❌ Invalid - unescaped quotes
{
  "message": "He said "hello" to me"
}

// ✅ Valid - escaped quotes
{
  "message": "He said \"hello\" to me"
}

// ❌ Invalid - unescaped backslash
{
  "path": "C:\Users\John"  // Only one backslash
}

// ✅ Valid - escaped backslashes
{
  "path": "C:\\Users\\John"  // Double backslashes
}

Valid escape sequences in JSON:

• \" - Double quote
• \\ - Backslash
• \/ - Forward slash (optional)
• \b - Backspace
• \f - Form feed
• \n - Newline
• \r - Carriage return
• \t - Tab
• \uXXXX - Unicode character

6. Match Opening and Closing Brackets

Mismatched brackets are harder to spot in large JSON files but cause immediate parsing failures.

Debugging strategy:

• Use an editor with bracket matching (most IDEs highlight matching pairs)
• Count opening vs. closing brackets: {{ }} and []
• Format your JSON - mismatched brackets become obvious
• Use a validator that shows the exact location of the mismatch

// ❌ Invalid - missing closing bracket
{
  "users": [
    {"name": "Alice"},
    {"name": "Bob"
  ]
}

// ✅ Valid - all brackets matched
{
  "users": [
    {"name": "Alice"},
    {"name": "Bob"}
  ]
}

7. Debug API Responses with Diff Tools

When API responses don't match expectations, use a diff tool to identify exactly what changed.

Use cases:

• Compare expected vs. actual API responses in tests
• Track changes between API versions
• Debug why a previously working integration broke
• Validate data transformations

Our JSON diff tool highlights added, removed, and modified values with precise path information.

8. Use JSONPath for Complex Data Extraction

When debugging issues in deeply nested JSON, use JSONPath to extract and isolate specific values quickly. For visual exploration of complex structures, use our JSON tree viewer to expand and collapse nodes interactively.

// Sample nested JSON
{
  "store": {
    "books": [
      {"title": "Book 1", "price": 12.99},
      {"title": "Book 2", "price": 8.99},
      {"title": "Book 3", "price": 15.99}
    ]
  }
}

// JSONPath queries
$.store.books[*].price     // Get all prices: [12.99, 8.99, 15.99]
$.store.books[0].title     // Get first book title: "Book 1"
$..price                   // Get all prices (deep search)

Test queries with our JSONPath tester to verify you're accessing the right data.

9. Validate Data Types

JSON parsing might succeed, but the data types could be wrong. This causes runtime errors that are harder to debug.

// JSON with type issues (still valid JSON!)
{
  "id": "123",           // Should be number: 123
  "active": "true",      // Should be boolean: true
  "price": "29.99",      // Should be number: 29.99
  "tags": "tag1,tag2"    // Should be array: ["tag1", "tag2"]
}

Prevention strategies:

• Use JSON Schema to define expected types
• Validate data types in your application code
• Add type checking in automated tests
• Use TypeScript with generated types from JSON

10. Leverage Browser Developer Tools

Modern browsers have excellent JSON debugging capabilities built into their developer tools.

Chrome DevTools tips:

• Network tab: View API responses with syntax highlighting and formatting
• Console: Use JSON.parse() with try-catch to test JSON strings
• Copy as cURL: Right-click requests to reproduce them for debugging
• Preserve log: Keep requests across page refreshes

// Quick validation in browser console
try {
  const data = JSON.parse(yourJsonString);
  console.log('Valid JSON:', data);
} catch (error) {
  console.error('Invalid JSON:', error.message);
  console.error('Error position:', error.message.match(/position (\d+)/)?.[1]);
}

Bonus: Common Error Messages Decoded

"Unexpected token" errors

What it means: The parser found a character it didn't expect at that position.

Common causes:

• Missing comma between properties
• Extra comma (trailing comma)
• Unquoted property names
• Single quotes instead of double quotes

"Unexpected end of JSON input"

What it means: The JSON ends prematurely.

Common causes:

• Missing closing bracket or brace
• Incomplete API response (network error)
• Truncated file

"JSON.parse: bad control character in string literal"

What it means: A string contains unescaped control characters.

Common causes:

• Literal newlines or tabs in strings (should be \n or \t)
• Unescaped backslashes
• Binary data in strings

Debugging Workflow Checklist

Follow this systematic approach when debugging JSON issues:

1. Validate syntax - Use a JSON validator to catch basic errors
2. Format the JSON - Beautify to make structure visible
3. Check common issues - Look for trailing commas, quote types, brackets
4. Verify data types - Ensure values match expected types
5. Test with samples - Create minimal reproducible examples
6. Use diff tools - Compare with known good versions
7. Isolate the problem - Remove sections until error disappears
8. Document the fix - Note what caused the issue for future reference

Tools for Efficient JSON Debugging

Keep these tools bookmarked for quick access:

• JSON Validator - First step for any JSON issue
• JSON Formatter - Make data readable
• JSON Diff - Compare versions
• JSONPath Tester - Extract specific values
• Schema Generator - Document expected structure

Conclusion

Effective JSON debugging is a skill that improves with practice and the right tools. By following these tips and using proper validation tools, you can reduce debugging time from hours to minutes. Remember: most JSON errors are simple syntax mistakes that validators catch instantly. Always validate first, format second, then debug systematically.

The key is to develop a consistent debugging workflow and use the right tool for each type of issue. Whether you're fixing a simple comma error or comparing complex API responses, having these techniques in your toolkit will make you a more efficient developer.