Working with APIs and JSON data is a daily routine for almost every web developer. However, a single missing comma, an unescaped character, or a misplaced bracket can freeze your application or break your API response completely.
Here are 5 of the most common JSON syntax errors developers encounter—and how you can quickly identify and fix them.
- Trailing Commas One of the most frequent mistakes is leaving a comma after the last key-value pair in an object or array. While JavaScript objects allow trailing commas, strict JSON standards do not.
❌ Incorrect:
JSON
{
"name": "Developer",
"role": "Frontend",
}
✅ Correct:
JSON
{
"name": "Developer",
"role": "Frontend"
}
- Single Quotes Instead of Double Quotes JSON specification strictly requires double quotes ("") for keys and string values. Using single quotes ('') will throw a parse error.
❌ Incorrect:
JSON
{
'status': 'active'
}
✅ Correct:
JSON
{
"status": "active"
}
- Unquoted Keys In JavaScript objects, quotes around keys are optional if they follow variable naming rules. In JSON, every single key must be enclosed in double quotes.
❌ Incorrect:
JSON
{
age: 25
}
✅ Correct:
JSON
{
"age": 25
}
- Unescaped Special Characters If your string value contains double quotes or backslashes, they must be properly escaped using .
❌ Incorrect:
JSON
{
"quote": "He said, "Hello World!""
}
✅ Correct:
JSON
{
"quote": "He said, \"Hello World!\""
}
- How to Validate & Format JSON Effortlessly Manually scanning hundreds of lines of minified JSON response is frustrating and wastes valuable development time.
To speed up your workflow, you can use our free online tool:
👉 Format and Validate your JSON on MarshMart Dev Tools
Why use this tool?
⚡ Instant Formatting: Convert messy or minified JSON into readable, beautifully indented structures instantly.
🔍 Real-Time Error Detection: Identifies exact line numbers where syntax errors occur.
🔒 100% Secure: All formatting happens client-side in your browser, keeping your data private.
Conclusion
Keeping your JSON clean and valid avoids unnecessary debugging hours. Bookmark your favorite validation tools and make JSON checking a part of your development checklist!
What other developer tools do you use daily to streamline your coding? Let me know in the comments below! 👇
