JSON Formatter & Validator

Format, validate & diff JSON — runs entirely in browser

FreeNo signupRuns in your browser

ToolJSON Formatter & Validator

All formatting happens in your browser — your JSON is never uploaded to a server.

Input

Output

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

How This Compares to Other Free JSON Tools

Feature	Typical online formatters	IDE/editor plugins
No signup required	Varies
Data never leaves your device
Structural diff between two JSON files	Varies	Varies
Convert to CSV, YAML, or TOML	Rare

TL;DR

Free JSON formatter and validator — pretty-print, minify, and validate JSON with syntax highlighting and precise error positions.
Handles large payloads locally in your browser; nothing is uploaded.

Pairs with

Starter kits

Run your projects on Claude Code?

We packaged the .claude config that runs this site — 26 specialist agents, 14 workflow skills, and 6 rule files from 31 real production incidents. From $9.

Get the Claude Code Production Pack — $29

Recommended partners

Dodo PaymentsAdd payments to your SaaS — try Dodo

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 this is 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 it

1
Paste your JSON into the input panel
2
Choose a mode — Format, Validate, Diff, or Convert
3
Formatted output appears instantly with syntax highlighting
4
Copy the result or download as a file

Frequently asked questions

Can it handle large JSON files?

Yes, it handles JSON files up to several MB efficiently. All formatting happens in your browser — your JSON is never uploaded to a server.

What formats can I convert between?

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

How does the diff feature work?

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

Does the validator show exactly where a syntax error is?

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.

Can I format minified JSON from an API response?

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.

Does converting JSON to CSV handle nested objects?

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.