You've tested your API locally, everything works perfectly. But in production, your API starts returning broken JSON. Your frontend crashes, users see errors, and you're left wondering: why does JSON break in real-world APIs?

Most tutorials explain what JSON is, but very few explain why APIs actually return broken JSON in production. In this guide, we'll explore the real-world causes of broken API JSON and show you how to fix it instantly using our free JSON Fixer tool.

Common Causes of Broken JSON in APIs

1. Trailing Commas from Backend Code

Many backend languages (Python, JavaScript) allow trailing commas, but JSON doesn't. When backend code generates JSON with trailing commas, it breaks JSON parsing.

❌ Broken API Response:

{
  "users": [
    {"id": 1, "name": "John"},
    {"id": 2, "name": "Jane"},  ← Trailing comma
  ]
}

2. Unescaped Characters in User Data

User-generated content with quotes, newlines, or special characters that aren't properly escaped breaks JSON structure.

❌ Broken API Response:

{
  "message": "User said "Hello World""  ← Unescaped quotes
}

3. Partial Responses from Network Issues

Network timeouts, connection drops, or server errors can result in incomplete JSON responses that are missing closing braces.

❌ Broken API Response (Truncated):

{
  "users": [
    {"id": 1, "name": "John"}
  ]
  ← Missing closing brace due to network timeout

4. Backend Logging Injected into JSON

Debug logs, error messages, or console output accidentally included in API responses corrupts JSON structure.

❌ Broken API Response:

DEBUG: Processing request...
{
  "status": "success"
}
ERROR: Request completed

5. Multiple JSON Objects Concatenated

Streaming responses or multiple API calls concatenated without proper array wrapping creates invalid JSON.

❌ Broken API Response:

{"id": 1}{"id": 2}{"id": 3}  ← Multiple objects, not an array

Real Broken API JSON Examples

Here are real-world examples of broken JSON from production APIs:

Example 1: E-commerce API with Trailing Comma

// API Response from /api/products
{
  "products": [
    {"id": 1, "name": "Laptop", "price": 999},
    {"id": 2, "name": "Mouse", "price": 25},  ← Trailing comma
  ]
}

Error: Unexpected token } in JSON

Example 2: User Profile API with Unescaped Quotes

// API Response from /api/user/123
{
  "name": "John O'Brien",
  "bio": "I love "coding" and "development""  ← Unescaped quotes
}

Error: Unexpected token c in JSON

How to Detect Broken JSON Quickly

Use JSON.parse() with Try-Catch

Wrap API responses in try-catch blocks to catch JSON parsing errors immediately.

Validate Before Processing

Use our JSON Validator to check API responses before using them in your application.

Check Response Headers

Verify Content-Type: application/json header is present.

How to Fix Malformed API JSON Using UnblockDevs

When you receive broken JSON from an API, don't waste time manually fixing it. Use our free JSON Fixer:

Copy the broken JSON from your API response
Paste it into our JSON Fixer tool
The tool automatically detects and fixes all errors
Copy the fixed JSON and use it in your application

Best Practices to Prevent Broken JSON

Backend Best Practices

Use proper JSON serialization libraries (don't build JSON manually)
Always validate JSON before sending API responses
Escape user-generated content properly
Set correct Content-Type headers
Handle errors gracefully without corrupting JSON structure

Frontend Best Practices

Always wrap JSON.parse() in try-catch blocks
Validate API responses before using them
Handle network errors and incomplete responses
Use our JSON Fixer as a fallback for broken responses

Fix Broken API JSON Instantly

Don't let broken API JSON break your application. Paste your API response into our free JSON Fixer and get it fixed in seconds.

Paste Your API Response into JSON Fixer

FAQ

Why does my API return broken JSON in production but not locally?

Production environments often have different error handling, logging, or network conditions that can corrupt JSON responses. Always validate API responses in production.

Can I automatically fix broken JSON from APIs?

Yes! Our JSON Fixer can automatically detect and fix most common JSON errors from API responses, including trailing commas, missing quotes, and unescaped characters.

Should I fix broken JSON on the frontend or backend?

Ideally, fix it on the backend to prevent the issue. However, use frontend validation and our JSON Fixer as a safety net for production issues you can't immediately fix.