Validate API JSON – Free Online API Response Validator
APIs power modern web and mobile applications, but even a small JSON error in an API response can break your entire application flow. Validate API JSON helps you instantly check whether an API response is valid JSON and safe to consume in frontend or backend systems.
Paste your API response JSON and validate it in real time — no uploads, no login, fully browser-based.
What is Validate API JSON?
Validate API JSON is a tool that checks whether an API response follows proper JSON syntax rules.
It verifies:
If your API response contains any syntax issues, the validator highlights them immediately.
Why Validate API JSON?
Validating API JSON is important because invalid responses can cause:
Application crashes
Invalid JSON causes runtime errors that break your app
JSON.parse() failures
Parser errors when trying to read API responses
Broken UI rendering
Frontend components fail to display data correctly
Data loss or incorrect state
Application state becomes corrupted or incomplete
Integration failures
Third-party services reject malformed JSON
By validating API JSON early, you can catch errors before they reach production.
When Should You Validate API JSON?
You should validate API JSON when:
Testing APIs during development
Ensure API endpoints return valid JSON
Debugging frontend API errors
Identify if the problem is with the API response
Working with third-party APIs
Verify external API responses are valid
Migrating legacy APIs
Check old API responses meet JSON standards
Validating mock API responses
Test your mocks before integration
QA testing API contracts
Verify API responses match specifications
How to Validate API JSON
Using this tool is simple:
Copy API Response
Copy the API response JSON from your request
Paste
Paste it into the input editor
Click Validate
Press the validate button
See Results
Instantly see valid or invalid status
Fix Errors
Fix any detected errors if needed
All validation happens instantly inside your browser.
Common API JSON Issues Detected
This tool detects common API-related JSON problems such as:
Invalid JSON syntax
Malformed JSON that violates syntax rules
Missing commas
Forgotten separators between properties
Unclosed braces or brackets
Missing } or ]
Invalid quotation marks
Single quotes instead of double quotes
Trailing commas
Extra comma at end of object or array
Unexpected tokens
Characters that don't belong in JSON
API responses returning HTML instead of JSON
Server error pages or redirect responses sent as JSON
Validate API JSON vs Fix Invalid JSON
| Feature | Validate API JSON | Fix Invalid JSON |
|---|---|---|
| Detect JSON errors | ✅ Yes | ✅ Yes |
| Auto-fix syntax | ❌ No | ✅ Yes |
| API-focused usage | ✅ Yes | ❌ No |
| Debugging support | ✅ Yes | ✅ Yes |
👉 If your API JSON is invalid, use Fix Invalid JSON to automatically repair it.
Is API JSON Validation Secure?
Yes.
Your API data never leaves your device. All validation is performed locally in your browser.
Private APIs
Safe for internal company APIs
Internal systems
Validate JSON used in internal tools
Sensitive application data
All JSON validation runs locally in your browser
Frequently Asked Questions
What is a valid API JSON response?
A valid API JSON response is one that follows JSON syntax rules and can be parsed successfully without errors.
Can I validate API responses from Postman or cURL?
Yes. Simply copy the response body from Postman, cURL, or browser DevTools and paste it here.
Does this tool validate API schemas?
No. This tool validates JSON syntax only, not schema or data rules.
Is this API JSON validator free?
Yes. It is completely free and works directly in your browser.