Question 1

What is JSON?

Accepted Answer

JSON (JavaScript Object Notation) is a lightweight, text-based data-interchange format defined in RFC 8259 and ECMA-404. It is the dominant format for REST APIs, configuration files, and data storage in web applications. JSON supports six value types: object, array, string, number, boolean, and null. Formatting (pretty-printing) adds indentation and line breaks to make compact JSON human-readable without changing the data — any valid parser produces identical results from formatted or minified input.

Question 2

How does JSON validation work?

Accepted Answer

JSON has strict syntax rules that differ from JavaScript object literals. Keys must be double-quoted strings ("key", not key or 'key'). Trailing commas after the last element are forbidden. Strings must use double quotes, not single quotes. Comments are not allowed. Only the six value types above are valid — undefined, functions, and NaN/Infinity are not valid JSON. This tool uses the browser's native JSON.parse() to validate — if the input is not valid JSON, the exact error message and position are displayed so you can pinpoint and fix the problem.

Question 3

Common JSON syntax errors

Accepted Answer

Most JSON validation failures come from a few recurring mistakes: Trailing commas — {"a": 1,} is invalid; remove the comma after the last property. Single quotes — {'key': 'value'} is invalid; JSON requires double quotes. Unquoted keys — {name: "John"} is invalid; wrap keys in double quotes. Comments — // comment and /* block */ are not allowed in standard JSON. Missing commas — forgetting a comma between array elements or object properties. If your JSON comes from JavaScript code, these are the most likely causes of parse errors.

Question 4

JSON minification

Accepted Answer

Minifying JSON removes all insignificant whitespace (spaces, tabs, newlines) to produce the smallest possible representation. A typical API response can shrink by 30–60% after minification. This matters for network performance: smaller payloads reduce Time to First Byte (TTFB) and improve mobile load times on slower connections. The savings are displayed after minification so you can see the exact size reduction. Note that minification works best alongside server-side gzip or Brotli compression — the two techniques are complementary, not redundant.

Question 5

JSON in REST APIs

Accepted Answer

JSON is the standard format for REST API request and response bodies, sent with the Content-Type: application/json header. When debugging API responses, paste the raw JSON here to instantly see the structure. Common tasks: verify the response shape matches your expected schema, check for null values in required fields, compare two API responses by formatting both with the same indentation, and validate webhook payloads before writing handler code.

Question 6

JSON vs JSON5 vs JSONC

Accepted Answer

Standard JSON is intentionally strict — no comments, no trailing commas, double quotes only. JSON5 is a superset that allows single quotes, unquoted keys, trailing commas, comments, and multi-line strings — useful for hand-edited config files. JSONC (JSON with Comments) is used by VS Code and TypeScript tsconfig.json; it allows // and /* */ comments but no other extensions. This tool validates strict JSON — if your input uses JSON5 or JSONC features, those extensions will be flagged as errors.

Question 7

How to format and validate JSON

Accepted Answer

Paste your JSON into the input field. Click Format to pretty-print it with your chosen indentation (2 spaces, 4 spaces, or tabs), or click Minify to remove all whitespace. If the JSON contains syntax errors, the exact error message and location are displayed so you can fix the issue. For API debugging, copy the raw response body directly from your browser DevTools Network tab or from tools like curl and Postman, and paste it here.

JSON Formatter

What is JSON?

How does JSON validation work?

JSON minification

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