JSON Formatter & Validator Online

About JSON Formatter

The 3STF JSON Formatter is a free, fast, 100% client-side tool that formats, validates, and minifies JSON with no signup, no ads, and zero data transmission. Every JSON operation runs inside your browser. Your tokens, API responses, and config files never leave your device. **What JSON formatting does** JSON (JavaScript Object Notation) is the dominant format for web APIs, configuration files, and data exchange. Raw JSON is typically minified (all whitespace stripped to save bandwidth), which makes it unreadable for humans. Formatting adds consistent indentation and line breaks so you can actually read the structure. Minifying does the reverse: strips all non-essential whitespace for production use, reducing file size by 20-40%. **Features** - **Format**: pretty-prints JSON with 2-space or 4-space indentation - **Minify**: strips all whitespace for compact output - **Validate**: parses JSON and shows precise error location on failure - **Syntax error highlighting**: errors show exact character position - **Big-input safe**: handles multi-MB JSON without freezing - **Copy-ready output**: one-click copy for pasting into your editor or terminal **Why client-side matters for JSON** API responses routinely contain sensitive data: authentication tokens, user PII, internal system IDs, business logic. Pasting that into a server-side JSON formatter is a data leak waiting to happen. Any tool that hits a remote endpoint could log, cache, or sell what you paste. The 3STF JSON Formatter uses your browser's native JSON.parse (the same parser your JavaScript code uses) to process input locally. There is no network call and no logging. Verify it yourself: open DevTools, click Format, observe zero network activity. **Common tasks this tool solves** - Debugging API responses during development - Reading webhook payloads (Stripe, GitHub, Shopify) - Inspecting JWT payload after decoding - Formatting `package.json`, `tsconfig.json`, `composer.json` - Minifying JSON for embedding in HTML data attributes - Validating that a string is well-formed before shipping it - Pretty-printing a GraphQL response **Understanding JSON structure** JSON consists of six types: objects, arrays, strings, numbers, booleans, and null. Objects use curly braces `{}`, arrays use square brackets `[]`. Trailing commas are not allowed (unlike JavaScript). Comments are not allowed. Keys must be strings in double quotes. Single quotes are invalid. If your input uses any of these non-standard features, the validator will flag exactly where the problem is. **When to minify** Minify JSON when embedding it in HTML (data attributes, inline scripts), storing it in databases, or transmitting it over bandwidth-constrained links. A typical API response shrinks 20-30% when minified. Formatting is for reading; minifying is for machines. **How it compares to jsonlint.com / jsonformatter.org** Those sites are full of ads, and most send your JSON to a server for processing. 3STF is ad-free and processes entirely in your browser. Same core features, better privacy, faster.