Developer / TOOLKIT
JSON Formatter & Validator
Format, validate, browse as a tree and convert JSON - side by side, in your browser.
Free to use · No account needed
Tip: append #data={...} to the URL to pre-fill JSON.
How to use
- Paste or type JSON on the left (or import a .json file, or pass it via
#data=in the URL). - Click Format to pretty-print side by side, Minify to compress, or Validate to check correctness - errors show the exact line and column.
- Switch the output to Tree to browse the JSON as a collapsible tree and click any value to copy it.
- Use the Convert dropdown for YAML or XML output, and Export to download the result as a file.
Reading minified JSON from an API response or config file is painful. This JSON formatter and validator beautifies ugly one-line JSON into an indented, readable tree, highlights syntax errors immediately, and can minify it back down for production. It is the standard companion for anyone working with REST APIs, configuration files, or data pipelines.
Use cases
1. Use case: Debug API responses Paste a minified JSON response from Postman or the browser network tab, format it, and read the structure clearly.
2. Use case: Review config files Open a large JSON configuration side by side, browse it as a tree, and convert it to YAML for documentation.
Practical tips
Pretty-print for reading, minify for shipping — same data, different whitespace. The most common parse errors are trailing commas, single-quoted strings and unquoted keys, all legal in JavaScript objects but illegal in JSON; the validator points at the exact position. Large files format fine locally since nothing is uploaded. Watch number precision on very long numeric IDs — converting JSON through a language that truncates them is a classic data bug. Like every tool on this site, the Json Formatter runs entirely in your browser: the data you enter never leaves your device, nothing is uploaded to a server, and the tool keeps working if your connection drops.
Common mistakes
JSON's rules are strict, and every deviation is a classic:
- Shipping pretty-printed JSON to production — minify for transport, pretty-print for reading.
- Writing single quotes or unquoted keys because JavaScript objects allow them; JSON does not.
- Leaving a trailing comma after the last element — the single most common validation error.
- Letting long numeric IDs pass through a language that truncates them to float precision, corrupting them silently.
Frequently asked questions
Does the Json Formatter send my data anywhere?
No. It runs entirely in your browser — your input is processed on your device and never uploaded. Refresh the page and it still works offline.