Written by Sam Taylor — Full-Stack Developer. More about me →After debugging JSON parse errors for over a decade, I can tell you the same five mistakes show up 90% of the time. Here they are, with the exact fix for each.
JSON does not allow a comma after the last item in an object or array. JavaScript objects do, which is why this trips people up constantly.
Wrong: {"name": "John", "age": 30,}
Right: {"name": "John", "age": 30}
JSON strings must use double quotes. Single quotes are valid in JavaScript and Python but not in JSON. This is the second most common error.
Wrong: {name: "John"}
Right: {"name": "John"}
All object keys in JSON must be double-quoted strings. JavaScript lets you skip quotes on keys; JSON does not.
JSON spec does not support comments. If you need documentation, use JSONC (VS Code variant) or add a separate documentation field like _comment.
Backslashes must be escaped in JSON strings. Windows file paths are the most common culprit: C:\Users\name should be C:\\Users\\name.
The fastest way to find these errors: paste your JSON into Formly JSON formatter and click Validate. It tells you the exact line and position of the first error.
Written by Sam Taylor — Full-Stack Developer. More about me →