D

JSON Formatter / Validator

Beautify, validate, and explore JSON with error line numbers and collapsible nodes.

Runs 100% in your browser — nothing is uploaded

About this tool

The JSON Formatter & Validator lets you instantly beautify minified JSON, validate structure, and pinpoint syntax errors down to the exact line and column. Paste raw JSON from an API response, a config file, or a log dump and get back cleanly indented, readable output in milliseconds — entirely inside your browser, with zero data sent to any server.

Unlike online formatters that relay your JSON through a backend (and may log or store it), this tool uses a pure JavaScript parser running locally. Open DevTools → Network while using it and you will see no outbound requests. That matters when you are working with API tokens, personal data, or internal configuration.

Indent level is configurable (2 or 4 spaces, or tabs). The validator surface shows a friendly error message for common mistakes — trailing commas, unquoted keys, single quotes, and mismatched brackets. Use the Paste Sample button to see a working example, Copy to copy the formatted output, and Clear to reset. Ideal for debugging REST API responses, editing package.json or tsconfig, or quickly reading minified production payloads.

Frequently asked questions

Does this tool send my JSON to a server?
No. The entire formatting and validation process runs in JavaScript inside your browser tab. Open DevTools → Network while using it — you will see zero outbound requests for the formatting operation.
Why does it say "Invalid JSON" for my data?
Common causes: trailing commas after the last item (not valid in JSON), single-quoted strings (JSON requires double quotes), JavaScript-style comments, or unquoted object keys. The error message will show the line and column where the problem was detected.
What is the maximum size of JSON I can format?
There is no hard limit imposed by this tool — it depends on your browser's available memory. Files up to several megabytes format instantly; very large files (100 MB+) may cause your browser tab to slow down.
Can I format JSON with comments (JSONC)?
Standard JSON does not allow comments. If your file has // or /* */ comments (JSONC or JSON5 style), strip them first. Support for JSONC parsing may be added in a future update.
How do I collapse or expand parts of the JSON tree?
Use the JSON Tree Viewer tool for interactive collapse/expand. The formatter outputs fully expanded indented text; the tree viewer gives you a collapsible node view.

Related tools

JSON Minifier

Strip whitespace from JSON to produce the smallest valid payload for APIs and storage.

JSON → YAML Converter

Convert JSON to YAML format instantly — using js-yaml, entirely in your browser.