JSON Formatter & Validator

What is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format derived from JavaScript object literals. It uses human-readable key/value pairs and ordered lists to represent structured data, and is described by RFC 8259. JSON supports six data types — strings, numbers, booleans, null, objects and arrays — and is language-independent: virtually every modern programming language can parse and produce it.

Because JSON is compact, easy to parse and directly compatible with JavaScript, it has become the de facto standard for web APIs, configuration files, NoSQL databases and inter-service communication. Whether you are reading a REST response, editing a package.json or inspecting a webhook payload, you are working with JSON.

Why format and validate JSON?

JSON that comes from an API or is generated by a machine is often minified to save bandwidth — it has no indentation and no line breaks. While efficient for transfer, this makes it hard to read and edit by hand. A formatter (also called a beautifier or pretty-printer) re-introduces consistent indentation, line breaks and spacing so the structure becomes visible at a glance.

Validation is equally important. A single misplaced comma, an unquoted key or a trailing comma can turn a JSON document into invalid syntax that fails to parse. A validator immediately tells you whether the document is well-formed and pinpoints the location of the error, so you can fix it before saving, deploying or sending the payload.

What this tool does

This JSON formatter and validator does three things in one pass:

• Validates — the input is parsed strictly. If it is invalid, you get a clear error message with the position of the problem.
• Beautifies — the parsed value is re-serialised with your chosen indentation (2 spaces, 4 spaces, tabs) so nested objects and arrays are easy to follow.
• Minifies — choose the "Minified" option to strip all whitespace, producing the smallest possible representation for storage or transfer.

The tool also reports the size of the input and output and the top-level type of the JSON value (object, array, string, number, boolean or null), which helps you quickly understand what you are working with.

When to use a JSON formatter

A JSON formatter is useful whenever you need to read, write or debug JSON by hand. Common scenarios include:

• Inspecting API responses. Paste a response body to read nested fields and verify the shape of the data.
• Editing configuration files. Many tools (eslint, tsconfig, package.json, VS Code settings) use JSON config; formatting keeps them readable.
• Debugging webhooks. Compare incoming payloads against expected schemas to find missing or mistyped fields.
• Preparing test fixtures. Pretty-print a fixture so collaborators can review and modify it without breaking the syntax.
• Minifying before deployment. Strip whitespace from embedded JSON to reduce payload size in production.

Common JSON pitfalls

JSON has a strict syntax, and a few mistakes account for most validation errors. Knowing them helps you write valid JSON faster:

• Trailing commas. A comma after the last item in an object or array is not allowed in strict JSON.
• Unquoted keys. Object keys must be wrapped in double quotes — single quotes and bare identifiers are invalid.
• Single-quoted strings. String values must use double quotes only.
• Comments. JSON does not support // or /* */ comments. Use a format like JSONC or JSON5 if you need them.
• Special number values. NaN, Infinity and -Infinity are not valid in JSON — use null or a string instead.
• Unescaped control characters. Literal tabs and newlines inside strings must be escaped as \t and \n.

When this tool reports an error, it usually points to one of these issues. Fix the highlighted position and re-format to confirm.