A single missing comma in a 500-line JSON file can bring your entire application down. JSON validation catches these errors before they hit production. Understanding the most common JSON mistakes saves hours of debugging and prevents embarrassing deployment failures.
What Is JSON Validator?
JSON validation checks that a string conforms to the JSON specification (RFC 8259). It verifies matching brackets, proper quoting, valid escape sequences, and correct data types. Our JSON Validator pinpoints the exact line and character where errors occur.
How to Use JSON Validator on DevToolHub
- Open the JSON Validator tool on DevToolHub — no signup required.
- Paste or enter your input data in the left panel.
- See the result instantly in the output panel.
- Copy the result or download it as a file.
The 5 Most Common JSON Errors
These mistakes account for 90% of JSON validation failures:
// 1. Trailing comma (INVALID)
{"name": "Alice", "age": 30,}
// 2. Single quotes (INVALID)
{'name': 'Alice'}
// 3. Unquoted keys (INVALID)
{name: "Alice"}
// 4. Missing comma between properties
{"name": "Alice" "age": 30}
// 5. Comments (INVALID in standard JSON)
{
"name": "Alice" // user name
}Standard JSON requires double quotes for strings and keys, no trailing commas, no comments, and commas between every property.
Pro Tips
- Validate JSON after every manual edit — even experienced developers introduce syntax errors
- Use a formatter after validation — valid JSON can still be hard to read
- If you need comments in config files, consider JSON5 or JSONC formats
- Pipe API responses through a validator during development to catch schema changes early
When You Need This
- Debugging malformed API responses before parsing
- Validating configuration files before deployment
- Checking JSON payloads in webhook integrations
- Verifying data exports before sending to partner systems
Free Tools Mentioned in This Article