How do I fix JSON validation errors?
Advanced Topics
By Dmitrii Kargashin · Updated February 2026
JSON syntax errors are easier to fix when you can see them clearly. The editor provides real-time error detection with clear messages, line numbers, and suggestions. This guide covers common validation errors and how to fix them.
Real-Time Error Detection
The editor highlights syntax errors as you type, with red squiggly underlines and detailed error messages when you hover.
Common JSON Errors & Fixes
❌ Missing or Extra Comma
❌ Incorrect:
{
"name": "Alice"
"age": 30
}✅ Correct:
{
"name": "Alice",
"age": 30
}Fix: Add comma between properties, but NOT after the last property.
❌ Unquoted Keys
❌ Incorrect:
{
name: "Alice",
age: 30
}✅ Correct:
{
"name": "Alice",
"age": 30
}Fix: All keys must be wrapped in double quotes.
❌ Single Quotes Instead of Double
❌ Incorrect:
{
'name': 'Alice',
'age': 30
}✅ Correct:
{
"name": "Alice",
"age": 30
}Fix: JSON requires double quotes (") not single quotes (').
❌ Trailing Comma
❌ Incorrect:
{
"name": "Alice",
"age": 30,
}✅ Correct:
{
"name": "Alice",
"age": 30
}Fix: Remove comma after the last property or array element.
❌ Mismatched Brackets
❌ Incorrect:
{
"items": [1, 2, 3}
]✅ Correct:
{
"items": [1, 2, 3]
}Fix: Match opening [ with closing ], and opening { with closing }.
❌ Comments in JSON
❌ Incorrect:
{
// This is a comment
"name": "Alice"
}✅ Correct:
{
"name": "Alice"
}Fix: Standard JSON doesn't support comments. Remove them or use JSONC format.
Error Location Tips
Check Line Numbers
Error messages include line and column numbers - use Cmd/Ctrl + G to jump directly to the error location.
Bracket Matching
Click next to a bracket - the editor highlights the matching bracket to help identify mismatched pairs.
Look Above the Error
Missing commas often report errors on the next line. Check the line above for missing commas.
Use Format to Auto-Fix
If JSON is valid but poorly formatted, use Format (Cmd/Ctrl + Enter) to reveal structure.
Quick Fix Workflow
Look for red squiggly underlines in the editor
Hover over the underline to read the error message
Apply the fix based on the error type
Verify the error disappears as you type
Pro Tip: Copy Valid JSON First
If you're struggling with errors in manually typed JSON, try copying a small valid JSON example first, then modify it. This ensures the basic structure is correct.
See also: JSON Schema validation
Still Have Questions?
Check out our other FAQ topics or return to the JSON Copilot app