Common JSON Syntax Errors That Break API Calls and How to Fix Them

A single stray character in a JSON request body is a frequent cause of API failures, often blamed on the server or client. The guide outlines the strict rules of valid JSON, which differ from JavaScript object literals, including required double quotes, no trailing commas, and no comments. It walks through five frequent mistakes, such as trailing commas, single quotes, unquoted keys, raw newlines in strings, and leading zeros, and shows the error messages a parser produces for each. It also recommends browser-based and JavaScript-based tools for formatting and validating JSON, while cautioning readers to check privacy practices before pasting sensitive data into online tools.