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JSON Formatter & Validator

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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.

Format or validate to see the output here.

How to use

  1. Paste or type JSON on the left (or import a .json file, or pass it via #data= in the URL).
  2. Click Format to pretty-print side by side, Minify to compress, or Validate to check correctness - errors show the exact line and column.
  3. Switch the output to Tree to browse the JSON as a collapsible tree and click any value to copy it.
  4. 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.

Boundary and failure cases

Strict JSON rejects trailing commas, single-quoted strings, comments and unquoted keys. If a payload validates here but fails in production, compare the byte stream: an HTTP client, a logging scrubber or a language binding that coerces 64-bit integers into floating point can change the document without changing the keys you notice first.

Very large numbers and high-precision decimals are common failure points. JavaScript Number cannot represent every integer beyond Number.MAX_SAFE_INTEGER. Tree views and some converters may round or stringify those values. When integrity matters, keep the original text and verify with a library that preserves BigInt or decimal types.

YAML and XML conversions on this page are convenience views, not lossless round-trips. Nested arrays, attribute-like keys and duplicate map keys can lose structure. Treat them as reading aids, then export from a purpose-built converter when you need a canonical file for another system.

Frequently asked questions

Does the Json Formatter send my data anywhere?

No. Formatting, validation and tree views run in your browser. Your JSON is not uploaded by this tool. Optional site analytics, when allowed, may record coarse operation events without the payload itself.

Why does my JSON validate here but fail in my application?
Most applications pass data through layers that alter it: number precision loss on large integers, charset conversion, or a parser that tolerates comments where strict JSON does not. Format the raw bytes here first, then compare the application's copy character by character.
How does the tool handle very large files?
Parsing and formatting run locally, so multi-megabyte files work within your device memory. Pretty-printing adds whitespace, so a minified API response can grow several times in size. That growth is expected, not a bug.
What happens when a string contains unescaped control characters?
Strict JSON requires control characters inside strings to be escaped. The validator reports the first offending line and column. Fix the source emitter rather than hand-editing production payloads when you can.
Can I convert JSON to YAML or XML safely?
Yes for reading. Use Convert for a readable view. Nested arrays and unusual key shapes are best-effort. Do not treat the converted text as a lossless archive of the original JSON.
Is duplicate key ordering preserved?
JSON objects are unordered maps in the formal model. This formatter keeps the order your browser's parser exposes when pretty-printing, which helps humans but is not a guarantee across every language runtime.
Is my JSON uploaded to a server?
No. Import, format, minify and tree view stay on this device. Closing or reloading the tab clears the working buffer.

Scenario guides

CSV to JSON

Convert between CSV and JSON.

Base64 Encoder / Decoder

Encode text and files.

JWT Decoder

Inspect JWT header and claims locally.

Hash Generator

MD5, SHA-1, SHA-256, SHA-512.

URL Inspector

Parse and edit query parameters locally.

Regex Tester

Validate patterns against sample JSON strings.