JSON Formatter, Validator & Viewer

A JSON validator checks whether a document is syntactically correct according to the JSON spec (RFC 8259) — matched brackets and braces, quoted keys, no trailing commas, and valid value types. This tool validates as you type using a hand-written parser that reports the exact line and column of any error, plus warnings for duplicate object keys, instead of a vague "unexpected token" message.

The best JSON formatter is one that's fast, free, and never uploads your data. This tool formats and validates JSON entirely in your browser, with a real code editor, a synced tree view, live XML/YAML/CSV conversion, and a compare-and-merge tool — no sign-up, no ads inside the workspace, and nothing you paste or drop ever leaves your device.

A JSON formatter is a tool that takes JSON text — often compact, minified, or inconsistently indented — and rewrites it with consistent line breaks, indentation, and spacing so a person can actually read it. It's the same idea as a code formatter, applied to JSON's object and array syntax.

It's a nod to how frustrating most online JSON tools are — cluttered with ads, forced sign-ups, and pages that quietly upload whatever you paste to a server. We built this one to not suck: no account, nothing ever uploaded, a real code editor instead of a plain textarea, and every feature (format, validate, convert, compare) in one workspace.

Yes. Parsing, formatting, validating, converting, and diffing all run locally in your browser using JavaScript — nothing you paste, upload, or drop is ever sent to a server. The one exception is "Fetch from URL," which makes a request directly from your browser to the address you provide, not through us.

Paste your JSON into the editor, upload a .json file, or drag one onto the page, then click "Format." It instantly pretty-prints the document with the indent width you choose (2, 3, 4 spaces, or a tab) — no separate "beautify" step needed.

The most common causes are a trailing comma before a closing bracket, an unquoted or single-quoted key, a missing comma between values, or a stray comment — none of which are valid in strict JSON. The editor underlines the problem inline and reports the exact line and column so you can jump straight to it.

Yes. Large documents are parsed and formatted in a background Web Worker, and the tree view loads nodes lazily as you expand them — so multi-megabyte files stay responsive instead of freezing the tab.

Paste your base document on the left and the incoming one on the right, then click "Compare." Both sides are parsed into JSON first, then walked structurally to list every added, removed, and changed value by key path. Check or uncheck each change to build a merged result, then copy or download it.

For objects, yes — the diff is computed by key path against the parsed JSON, not by text position, so reordering an object's keys with the same values produces no diff entries. Array order does matter, though: array items are compared by index, so reordering elements inside an array is reported as a change.

A raw text diff (like a plain line-by-line diff) flags any line that moved or was reformatted differently, even when the underlying data is identical. This tool always parses both documents into JSON before diffing, then compares the resulting structures by key path — so whitespace, indentation, and object key order never create noise; only genuine value differences show up.

Yes. Pick XML, YAML, or CSV from the "View" dropdown next to the tree for a live conversion that updates as you edit — no separate "Convert" button. Click "Minify" to collapse the same document to the smallest valid single-line representation.

Format pretty-prints your JSON with the indent width you choose (spaces or a tab). Minify strips all non-essential whitespace down to the smallest valid representation — useful right before you ship it over the wire.

JSON was deliberately designed as a minimal, unambiguous data-interchange format, not a config language — leaving out comments and trailing commas keeps every parser, in every language, byte-for-byte compatible with the same spec (RFC 8259). This tool enforces that strict spec, so any document that validates here will also parse cleanly in Python, JavaScript, or any other language's JSON parser.

No. There’s no sign-up, no login, and no paid tier — the tool is free to use for everyone.

The document is compressed and encoded directly into the URL fragment (the part after #), which browsers never send to a server on navigation. Anyone you send the link to decodes it locally too.

Running the tool costs nothing to you because a small, unobtrusive ad banner supports it — ads never appear inside the editor, tree view, or convert/compare panels, only around the marketing sections.

Possibly — JSON numbers are parsed as standard JavaScript numbers, so integers larger than 2^53 (about 9 quadrillion) can lose precision. This is true of any browser-based JSON tool, not just this one. If exact large IDs matter, keep them as quoted strings in your source data.

Not directly — the tree is for browsing and searching. Make your edits in the code editor on the left and they'll appear in the tree instantly.

We'll warn you before you navigate away with unsaved changes, but nothing is auto-saved between browser sessions yet — copy, download, or grab a share link if you want to keep your work.

Yes, once the page has loaded. The only feature that needs a live connection is "Fetch from URL," since it has to reach the address you give it.