Common JSON Errors and How to Fix Them

JSON looks similar to a JavaScript object literal, but the rules are narrower. Property names must use double quotes, string values must use double quotes, comments are not allowed, and special values such as undefined, NaN, and Infinity are not part of the JSON format.

This difference explains why a value copied from source code can work inside an application but fail when pasted into an API request, configuration file, or JSON parser. Start by checking the syntax rather than assuming the data itself is wrong.

A trailing comma is one of the most frequent errors. The text {"name":"John",} contains a comma after the final property, so a strict JSON parser rejects it. Remove the final comma while keeping commas between properties and array items.

The opposite problem also occurs: two properties may be placed next to each other without a comma. Parser messages often point near the second property because that is where the parser discovers that the expected separator is missing.

A quote inside a string must be escaped with a backslash. For example, a message containing a quoted word needs to use \” inside the JSON string. Backslashes used in file paths and regular expressions may also require escaping.

Literal line breaks cannot appear inside an ordinary JSON string. Represent them with \n, or use an array of strings when the content is naturally divided into lines. If copied text contains smart quotes, replace them with standard double-quote characters.

Objects use braces and contain named properties. Arrays use brackets and contain ordered values. A missing closing brace or bracket can make the error appear far from the actual mistake, especially in a deeply nested payload.

JSON supports strings, numbers, booleans, null, arrays, and objects. Dates are normally represented as strings, and large integers may lose precision when an application converts them to JavaScript numbers. Validate both the syntax and the expected data type for each field.

Paste the smallest failing payload into a formatter, read the first parser error, and inspect the characters immediately before that location. Fix one error at a time because a malformed quote or missing bracket can cause several misleading follow-on errors.

Formatting only improves structure and readability. It does not remove secrets. Before sharing a corrected payload, delete access tokens, session identifiers, customer data, internal URLs, and any other values that should not leave your environment.