Loading...
Loading...
Free online JSON formatter and validator — format, minify, and validate JSON with tree view. Perfect for API responses and config files.
JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format that is easy for humans to read and write and easy for machines to parse and generate. It is language-independent but uses conventions familiar to programmers of C-family languages, making it the default choice for web APIs, configuration files, and data storage across virtually every modern programming language and platform.
JSON supports six data types: strings (double-quoted Unicode text), numbers (integer and floating-point, no leading zeros), booleans (true/false), null, objects (unordered key-value collections enclosed in {}), and arrays (ordered value lists enclosed in []). This simple yet expressive type system can represent almost any data structure.
Validation is critical because JSON parsers are strict. A trailing comma, a single-quoted string, or a missing closing brace will cause the entire parse to fail. Unlike JavaScript object literals, JSON requires double quotes for all keys and string values, does not allow comments, and has no support for undefined, functions, or date objects. This strictness is what makes JSON universally portable.
Formatting and minification serve complementary purposes. Formatted JSON uses indentation and whitespace to make the structure visually clear — essential for development, debugging, and code review. Minified JSON removes all unnecessary whitespace, reducing file size by 30-50% for faster network transmission. Most production APIs return minified JSON; developers use formatters to inspect it.
JSON has become the lingua franca of web APIs, replacing XML in most modern applications. Its simplicity, native support in JavaScript (JSON.parse/JSON.stringify), and widespread library support in every language make it the default choice for data interchange. However, for very large datasets, consider alternatives like Protocol Buffers or MessagePack that offer faster parsing and smaller serialized sizes while remaining interoperable.
JSON Schema is a powerful companion specification that describes the structure, content, and validation rules for JSON documents. Using JSON Schema, you can define required fields, specify data types, set numeric ranges, enforce pattern constraints on strings, and describe complex nested structures. Many API frameworks integrate JSON Schema to automatically validate request and response bodies against predefined contracts, catching structural errors early in development and serving as living documentation for your data interfaces.
JSON requires double quotes for keys and string values, does not allow trailing commas, comments, or functions, and has a strict set of data types. JavaScript objects are more permissive in all aspects. Valid JSON is always valid JavaScript (when parsed as an expression), but not all JavaScript objects are valid JSON.
Most common causes: (1) trailing commas in objects or arrays, (2) single quotes used instead of double quotes for keys or strings, (3) missing quotes on object keys, (4) unmatched brackets or braces, (5) leading zeros in numbers, and (6) comments (JSON does not support comments — use a separate metadata field instead).
Minification removes all whitespace, newlines, and indentation from JSON, producing the most compact representation possible. Use minified JSON in production API responses and configuration files to reduce bandwidth and parse time. Use formatted JSON during development for readability.
Strict JSON does not support comments. If you need annotations, use a convention like a special '_comment' key or use JSONC (JSON with Comments) which is supported by some tools but not standard. For configuration files, consider alternatives like YAML or TOML that natively support comments.
JSON itself has no size limit, but practical limits depend on the parser and available memory. Browsers typically handle JSON responses up to 100MB. For larger payloads, consider streaming parsers (like JSON.parse in chunks) or alternatives like NDJSON (newline-delimited JSON) or Protocol Buffers.
JSON Schema is a vocabulary that allows you to annotate and validate JSON documents using JSON itself. It describes the expected structure, data types, and constraints for a document. JSON Schema is used in API development to validate request and response payloads, in form builders to define validation rules, and in configuration validation tools to catch structural errors before runtime.
For files over 50MB, avoid loading the entire document into memory. Use streaming JSON parsers that process tokens incrementally — libraries like ijson (Python), SAX-style parsers (Java), or streaming parse methods in Node.js. For analysis without full loading, tools like jq allow you to query and filter large JSON files using a concise query language.