Essential terminology for working with JSON data — from basic concepts to advanced specifications.
This glossary covers 35+ essential JSON terms that every developer should know. Whether you are just starting with JSON or need a quick reference for advanced concepts like JSON Schema or JWT, this guide has you covered. Terms are organized alphabetically for easy navigation.
A set of protocols and tools that allow different software applications to communicate with each other. REST APIs commonly use JSON as the data format for requests and responses. When you call an API endpoint, you often send JSON data and receive JSON data back.
An ordered collection of values enclosed in square brackets []. Arrays can contain any valid JSON values including strings, numbers, objects, other arrays, booleans, or null. Array elements are accessed by their zero-based index position. Example: ["apple", "banana", "cherry"]
A binary-to-text encoding scheme that represents binary data using 64 ASCII characters. Base64 is commonly used to embed binary data (like images or files) within JSON, since JSON only supports text. The encoded data is larger than the original but safe for text-based transmission.
A data type with only two possible values: true or false. In JSON, boolean values must be lowercase and are not enclosed in quotes. Booleans are used for flags, toggles, and conditional data.
An HTTP header that indicates the media type of the request or response body. For JSON data, the correct Content-Type is application/json. Setting this header correctly ensures that servers and clients parse the data properly.
The official standard that defines the JSON data interchange syntax, published by ECMA International. ECMA-404 is a minimal specification that describes only the syntax rules, making JSON language-independent and universally applicable across programming environments.
A combination of characters used to represent special characters within JSON strings. Common escape sequences include \" for double quotes, \\ for backslash, \n for newline, and \t for tab. Unicode characters can be escaped using \uXXXX format.
A lightweight, text-based data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. Despite its name, JSON is language-independent and widely used across all modern programming languages for APIs, configuration files, and data storage.
A vocabulary for annotating and validating JSON documents. JSON Schema allows you to define the expected structure, data types, required fields, and constraints for your JSON data. It is widely used for API documentation, form validation, and ensuring data consistency.
A query language for selecting and extracting data from JSON documents. Similar to XPath for XML, JSON Path uses expressions like $.store.book[0].title to navigate nested structures and retrieve specific values or arrays of values.
A string syntax defined in RFC 6901 for identifying a specific value within a JSON document. Unlike JSON Path, JSON Pointer uses a simple slash-separated format like /store/book/0/title and references exactly one value rather than querying for multiple matches.
A method of encoding Linked Data using JSON. JSON-LD is used extensively for structured data markup on websites (Schema.org), enabling search engines to understand page content. It adds semantic meaning to JSON through context definitions and typed values.
An extension of JSON that allows comments, trailing commas, unquoted keys, single-quoted strings, and other JavaScript-like syntax. JSON5 is designed to be more human-friendly for configuration files while remaining a superset of standard JSON.
A variant of JSON that allows JavaScript-style comments (// line comment and /* block comment */). JSONC is commonly used in VS Code settings files and other configuration contexts where documentation within the file is helpful.
A compact, URL-safe token format used for securely transmitting information between parties. JWTs consist of three Base64-encoded parts: a header (algorithm and token type), a payload (claims/data), and a signature. They are widely used for authentication and authorization in web applications.
The identifier in a key-value pair within a JSON object. In JSON, keys must always be strings enclosed in double quotes. Keys are used to access their corresponding values, similar to property names in programming. Example: in {"name": "John"}, "name" is the key.
The process of analyzing JSON code for potential errors, stylistic issues, and deviations from best practices. A JSON linter checks for syntax errors, inconsistent formatting, and common mistakes. Linting helps catch problems early before they cause runtime errors.
A standardized identifier that indicates the nature and format of a file or data. The official MIME type for JSON is application/json. This is used in HTTP headers, file type detection, and content negotiation to ensure proper handling of JSON data.
The process of removing all unnecessary whitespace, line breaks, and indentation from JSON to reduce file size. Minified JSON is harder for humans to read but transfers faster over networks and uses less storage. It is the opposite of pretty-printing.
A format where each line contains a valid JSON value, separated by newline characters. Also known as JSON Lines (.jsonl), NDJSON is ideal for streaming data, log files, and processing large datasets line by line without loading the entire file into memory.
A JSON object contained within another JSON object or array. Nesting allows you to represent complex, hierarchical data structures. There is no technical limit to nesting depth, but deeply nested structures can be difficult to work with and may indicate a need for data model redesign.
A special value representing the intentional absence of any value. In JSON, null must be lowercase and is not enclosed in quotes: null. It is distinct from an empty string, zero, or an undefined/missing key.
A JSON data type representing numeric values. JSON numbers can be integers or floating-point, positive or negative, and may use exponential notation. Numbers are not enclosed in quotes. Example values: 42, -17.5, 3.14e10
An unordered collection of key-value pairs enclosed in curly braces {}. Each key must be a unique string within the object, and values can be any valid JSON type. Objects are the primary structure for representing records, configurations, and entities in JSON.
The process of converting a JSON string into a native data structure that a programming language can work with. In JavaScript, this is done with JSON.parse(). Parsing validates the JSON syntax and transforms text into objects, arrays, and primitive values.
The actual data content being transmitted in an API request or response, as opposed to headers or metadata. In REST APIs, the JSON payload typically contains the business data being created, updated, or retrieved. In JWTs, the payload section contains the claims.
The process of formatting JSON with indentation, line breaks, and spacing to make it human-readable. Pretty-printed JSON is easier to read and debug but larger in file size. Most JSON formatters default to 2 or 4 space indentation.
An architectural style for designing networked applications. RESTful APIs use HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources, with JSON being the most common data format for request and response bodies.
The data portion of an HTTP response, separate from the status code and headers. In JSON APIs, the response body contains the JSON-formatted data returned by the server, such as requested resources, operation results, or error details.
The current Internet Standard (STD 90) that defines the JSON data interchange format. Published by the IETF, RFC 8259 supersedes earlier specifications and is the authoritative reference for JSON syntax, encoding requirements (UTF-8), and interoperability guidelines.
The process of converting a data structure or object into a format suitable for storage or transmission, typically a JSON string. Deserialization is the reverse process. Together, they enable data exchange between different systems, languages, and platforms.
A sequence of Unicode characters enclosed in double quotes. Strings are the most versatile JSON data type, used for text, identifiers, dates, and any data that should be treated as text. Special characters within strings must be escaped.
The process of converting a native data structure into a JSON string. In JavaScript, this is done with JSON.stringify(). Stringification is the opposite of parsing and is used when preparing data for storage, transmission, or display.
A universal character encoding standard that assigns a unique number to every character across all writing systems. JSON strings support the full Unicode character set, allowing representation of text in any language. Characters outside the Basic Multilingual Plane can be represented using surrogate pairs.
The default and recommended character encoding for JSON documents. UTF-8 is a variable-width encoding that efficiently represents all Unicode characters. Per RFC 8259, JSON text exchanged between systems that are not part of a closed ecosystem must be encoded in UTF-8.
The process of checking whether a JSON document conforms to correct syntax (syntactic validation) or matches an expected structure defined by a schema (semantic validation). Validation catches errors before they cause problems in applications.
The data associated with a key in a JSON object, or an element within a JSON array. A value can be a string, number, boolean, null, object, or array. Values are what you actually store and retrieve when working with JSON data.
Put your JSON knowledge into practice with our free tools:
Dive deeper with our blog tutorials: