Common JSON Errors and How to Fix Them

JSON (JavaScript Object Notation) is the de facto standard for data exchange on the web. It is lightweight, readable, and easy to parse. However, JSON is notoriously strict about its syntax. Even a single misplaced character will cause a parser to throw an error. Here are the most common JSON errors and how to resolve them.

1. The Trailing Comma Error

The Error: `Unexpected token ] in JSON at position...`
The Cause: Unlike JavaScript arrays or objects, JSON does not allow a comma after the final element in an array or object.
The Fix: Remove the last comma.
*Invalid:*
```json
{
"name": "John",
"age": 30,
}
```
*Valid:*
```json
{
"name": "John",
"age": 30
}
```

2. Unquoted or Single-Quoted Keys

The Error: `Unexpected token a in JSON at position...`
The Cause: All keys (property names) in a JSON object must be wrapped in double quotes (`"`). Single quotes (`'`) or unquoted keys are invalid.
The Fix: Wrap all keys in double quotes.
*Invalid:*
```json
{
name: 'John'
}
```
*Valid:*
```json
{
"name": "John"
}
```

3. Using Single Quotes for Strings

The Error: `Unexpected token ' in JSON at position...`
The Cause: Just like keys, all string values in JSON must use double quotes. Single quotes are not supported.
The Fix: Replace single quotes with double quotes for all string values.

4. Unescaped Characters

The Error: `Unexpected token ... in JSON`
The Cause: If your string contains a double quote, a backslash, or a control character (like a newline), it must be properly escaped.
The Fix: Use a backslash (`\`) to escape special characters. For example, a double quote inside a string should be written as `\"`.
*Invalid:*
```json
{
"quote": "He said, \"Hello!\""
}
```
*Valid:*
```json
{
"quote": "He said, \\"Hello!\\""
}
```

5. Missing Commas

The Error: `Unexpected string in JSON at position...`
The Cause: Forgetting to separate elements in an array or key-value pairs in an object with a comma.
The Fix: Ensure every element (except the last one) is followed by a comma.

Conclusion

Debugging JSON manually can be tedious, especially with large files. To quickly find and fix syntax issues, use an online JSON Formatter and Validator. These tools will instantly pinpoint the exact line and character where the error occurred, saving you valuable development time.