JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language Standard but is language-independent. JSON has largely replaced XML in modern web APIs (REST, GraphQL) due to its simplicity and lower overhead. JSON sample files are indispensable for testing API endpoints and data serialization libraries. Developers use them to verify that their applications can correctly parse complex data structures, including nested objects and arrays. They are also used to test configuration loading mechanisms and to validate that error handling logic works correctly when encountering invalid or huge JSON payloads.