What is the most common JSON syntax mistake?

Trailing commas and incorrect quoting are among the most common JSON failures, especially when snippets are copied from JavaScript.

How do I fix JSON errors faster?

Validate the payload first to find the break point, then format the corrected version to make the structure easier to review.

Guide

Most invalid JSON issues come from a small set of repeated syntax mistakes.

Direct Answer

Look for missing double quotes, trailing commas, missing colons, unmatched brackets, and raw control characters first.

JSON does not allow a comma after the last property in an object or the last item in an array.

This is a common mistake when data is copied from JavaScript or edited manually.

{
  "name": "StructKit",
  "mode": "format",
}

JSON requires double quotes around keys and string values. Single quotes are valid in some programming languages, but not in JSON.

{'name': 'StructKit'}

Run the payload through a validator to locate the break point, then reformat the corrected payload to confirm the structure is stable.

If the JSON came from a template, inspect the data-generation step rather than fixing the output manually every time.