5 Common JSON Errors That Break APIs (and How to Fix Them)

Rohit Mittal — Wed, 13 May 2026 10:00:41 +0000

5 Common JSON Errors That Break APIs (and How to Fix Them)

If you’ve worked with APIs for even a short time, you’ve probably run into this:

“Why is this JSON not working?!”

Everything looks fine… until your parser throws an error and your app breaks.

The truth is, most JSON issues are small but deadly — a missing comma, a trailing bracket, or an incorrect structure can completely break your API flow.

In this post, I’ll walk through the 5 most common JSON errors developers face, along with simple fixes and examples.

1. Missing Commas Between Fields

This is probably the most common issue.

❌ Invalid JSON:

{
  "name": "John"
  "age": 30
}

✅ Fixed JSON:

{
  "name": "John",
  "age": 30
}

Why it happens:
When manually editing JSON, it’s easy to forget commas between key-value pairs.

2. Trailing Commas

Some languages allow trailing commas — JSON does NOT.

❌ Invalid JSON:

{
  "name": "John",
  "age": 30,
}

✅ Fixed JSON:

{
  "name": "John",
  "age": 30
}

Tip:
If you're copying JSON from JavaScript objects, watch out for this.

3. Unquoted Keys or Strings

JSON requires double quotes for keys and string values.

❌ Invalid JSON:

{
  name: "John",
  age: 30
}

✅ Fixed JSON:

{
  "name": "John",
  "age": 30
}

4. Incorrect Data Types

Sometimes values are accidentally wrapped as strings instead of numbers or booleans.

❌ Problematic JSON:

{
  "isActive": "true",
  "count": "10"
}

✅ Better JSON:

{
  "isActive": true,
  "count": 10
}

Why it matters:
Your backend or frontend logic may behave incorrectly if types are wrong.

5. Unclosed Brackets or Braces

This is another classic.

❌ Invalid JSON:

{
  "user": {
    "name": "John"

✅ Fixed JSON:

{
  "user": {
    "name": "John"
  }
}

How to Fix JSON Faster

Manually debugging JSON is frustrating — especially with large API responses.

A better approach is to use a tool that can:

Validate JSON instantly
Highlight errors
Format and beautify the structure
Fix common issues automatically

I’ve been using a simple tool called Fixzi for this:

👉 https://fixzi.ai/json-validator

It helps quickly:

Validate JSON
Fix invalid structures
Format and clean large payloads
Compare JSON responses (useful for APIs)

Final Thoughts

JSON errors are small, but they can cause big production issues — especially when working with APIs, webhooks, or third-party integrations.

If you’re debugging JSON frequently:

Always validate before using it
Use proper formatting tools
Avoid manual edits when possible

If you’ve faced other tricky JSON issues, I’d love to hear them 👇

DEV Community: Rohit Mittal

5 Common JSON Errors That Break APIs (and How to Fix Them)