Free JSON Formatter & Validator Online

Remove the comma after the last property. JSON does not allow trailing commas, unlike JavaScript.

Use double quotes for all strings and property names. Single quotes are not valid JSON.

All object keys must be quoted: {"key": "value"}.

JSON has no undefined or NaN types. Use null for missing values.

JSON does not support comments. Remove them or use a format like JSONC for config files.

• Debugging API responses
• Reading config files
• Code reviews and documentation
• Exploring unfamiliar data structures

• Sending data in API requests
• Storing in databases
• Reducing payload size for production
• Embedding JSON in HTML attributes

const data = JSON.parse('{"name": "Alice", "age": 30}');
console.log(data.name); // "Alice"

Throws SyntaxError if the string is not valid JSON. Always wrap in try/catch when parsing user input or API responses.

const obj = { name: 'Alice', scores: [95, 87, 92] };
const json = JSON.stringify(obj, null, 2); // null = no replacer, 2 = indent

The second argument filters keys (pass null to keep all). The third argument sets indentation — use 2 for readability, omit for minified output.

const res = await fetch('https://api.example.com/data');
const data = await res.json(); // parses JSON automatically

res.json() is shorthand for res.text() → JSON.parse(). It throws if the response body is not valid JSON.

The dominant format for web API payloads. Content-Type: application/json signals JSON encoding. Most HTTP client libraries (Axios, Fetch API, requests, Guzzle) parse JSON responses automatically. Pagination typically uses a wrapper object with "data", "meta", and "links" keys (JSON:API spec) or a flat response with "items" and "nextCursor".

Node.js project configuration and dependency manifest. Uses JSON5-extended rules in some tooling but must be strictly valid JSON. The scripts object defines npm run commands; dependencies and devDependencies use semver ranges. Processed by the npm CLI — never needs to be parsed manually by your code.

TypeScript compiler configuration. Unusually, this file supports JavaScript-style comments (// and /* */) and trailing commas despite using the .json extension. TypeScript's parser handles these JSON5 extensions internally. This is why linters sometimes complain about tsconfig.json being "invalid JSON".

Browser storage only holds string values. Storing objects requires JSON.stringify() on write and JSON.parse() on read. A common bug is forgetting to parse on retrieval — comparing a stored boolean with true will always fail if the value was stored as the string "true". Always pair storage and retrieval with the same serialization approach.

PostgreSQL natively stores and indexes JSON in JSONB (binary JSON) columns. You can query nested properties with -> and ->> operators, index specific keys with GIN indexes, and update individual paths. JSONB is preferred over the older JSON type because it stores data in binary form (faster queries) and deduplicates object keys.

Real-time protocols commonly use JSON-encoded messages. WebSocket frames carry raw bytes — JSON.stringify/parse handles encoding. Server-Sent Events use a "data: {...}\n\n" format where the data field contains a JSON string. For high-frequency messages (gaming, financial data), consider MessagePack or Protocol Buffers as more compact binary alternatives.