JSON Formatter & Validator

Format, validate & diff JSON — runs entirely in browser

DeveloperFREEYour data never leaves your browser

100% freeNo signupRuns in your browser

JSON Formatter & Validator is a free, browser-based tool that lets you format, validate & diff json — runs entirely in browser — with zero signup, zero installation. Your data never leaves your browser. Part of 116+ free developer and business tools at wowhow.cloud, built and maintained by a team with 14+ years of hands-on development experience.

TOOLJSON Formatter & Validator

Input

Output

{
  "name": "WOWHOW",
  "type": "digital marketplace",
  "products": 150,
  "categories": [
    "AI Prompts",
    "Templates",
    "Tools"
  ],
  "active": true,
  "metadata": null
}

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About JSON Formatter & Validator

JSON (JavaScript Object Notation) is the lingua franca of modern APIs, config files, and data interchange. While the JSON specification defined in RFC 8259 is simple, real-world JSON from APIs is often minified, contains trailing commas from hand-editing, or has subtle type mismatches that cause runtime errors. A proper formatter does more than add whitespace — it validates against the spec, pinpoints parse errors with exact line and column numbers, and converts between JSON and adjacent formats like CSV, YAML, and TOML.

How It Works

The formatter parses your input using the browser's native JSON.parse(), which implements the RFC 8259 specification exactly. If parsing fails, the caught SyntaxError message is surfaced with the error position mapped to a human-readable line and column number.

Formatting applies JSON.stringify() with a configurable indent parameter (2 or 4 spaces). The diff engine runs a structural deep-equality comparison between two parsed objects, walking the key tree recursively to identify added keys (in the new object only), removed keys (in the original only), and changed values (same key, different value). Results are rendered with color-coded annotations.

Format conversion to CSV flattens the JSON object tree using dot-notation keys, maps each root array element to a row, and writes RFC 4180-compliant comma-separated output. YAML conversion maps JSON primitives, arrays, and objects to their YAML equivalents following the YAML 1.2 specification.

Who Is This For

A backend engineer debugging a third-party webhook response pastes the raw minified payload to expand and inspect the structure without writing a script.

A frontend developer compares two API response snapshots to identify which fields changed after a backend deployment broke the UI.

A DevOps engineer converts a JSON config exported from one service into YAML format before importing it into a Kubernetes ConfigMap.

A QA analyst validates that a JSON fixture file contains no syntax errors before committing it to a test suite, catching a missing closing brace immediately.

How to Use

Paste your JSON into the input panel

Choose a mode — Format, Validate, Diff, or Convert

Formatted output appears instantly with syntax highlighting

Copy the result or download as a file

Frequently Asked Questions

Yes, it handles JSON files up to several MB efficiently. Processing happens entirely in your browser.

JSON to CSV, YAML, and TOML — and the reverse. The tool auto-detects the input format.

Paste two JSON objects and see a structural diff — added, removed, and changed keys are highlighted in green and red.

Yes. When the JSON is invalid, the error message includes the line number and column position of the first parse failure, so you can jump directly to the problem rather than scanning the whole document.

Absolutely. Paste any single-line minified JSON and the formatter expands it with proper indentation and line breaks. This is one of the most common use-cases — inspecting compressed API payloads while debugging.

Nested objects are flattened using dot notation (e.g., address.city becomes a column header). Arrays of primitives are joined with semicolons. Deeply nested structures may need manual cleanup, but flat and one-level-deep JSON converts cleanly.