JSON Formatter & Viewer

Format JSON pages & paste-in JSON: highlighting, collapsible tree, validation, repair & error detection. Fast, private.

Make every JSON page instantly readable — and edit your own JSON too. JSON Formatter automatically turns raw, unreadable JSON responses into clean, syntax-highlighted, explorable data with a collapsible tree, error detection, and clickable links. And when you want to work on JSON yourself, click the icon to open a full paste-in formatter that validates, repairs, minifies, and beautifies. It works on any JSON page no matter the URL, and stays completely out of the way on normal pages. FEATURES • Paste-in JSON formatter & editor — click the extension icon to open a full editor: paste, type, or drop a file, then format, validate, minify, or beautify it instantly. • One-click Repair — fixes the most common JSON mistakes automatically: comments, single quotes, unquoted keys, and trailing commas. • Instant validation with precise errors — invalid JSON shows the exact line and column plus a plain-English explanation of what went wrong. • "About this JSON" insights — see byte size, key/object/array counts, nesting depth, a value-type breakdown, duplicate-key warnings, and minify savings. • Minify & Expand, your way — collapse to a single line or pretty-print, sort keys alphabetically, and choose 2-space, 4-space, or tab indentation. • Edit in JSON Formatter — on any auto-formatted JSON page, one click sends that JSON straight into the editor so you can tweak it. • Session history — recent inputs are kept locally so you can jump back to earlier JSON. • Three views, switchable on the page — Formatted (pretty + syntax highlighted), Tree (collapsible, with indent guides), and Raw (untouched source). • Collapsible tree with indent guides — expand and collapse objects and arrays, or use Expand all / Collapse all. Large documents render lazily so it stays fast. • Syntax highlighting — keys, strings, numbers, booleans and null are colour-coded for fast scanning. • Clickable URLs — http(s) values become links that open in a new tab. • Works on any JSON page — detection is by response content type, not the URL, so it formats APIs, endpoints and .json files alike. • Import, Copy & Download — load .json, .txt, .ndjson, .har and more; copy the result or download it as a .json file in one click. • Dark mode — choose Light, Dark, or Match browser/system in the settings. It follows your system theme automatically. • Fast and private — everything runs locally in your browser. Nothing is uploaded, and there is a negligible (sub-millisecond) impact on non-JSON pages. HOW TO USE Open any URL that returns JSON and the page is formatted automatically — use the toolbar to switch between Formatted, Tree and Raw, expand/collapse the tree, copy, or download. On a formatted page, click "Edit in JSON Formatter" to send that JSON to the editor. To work on your own JSON, click the extension icon to open the JSON Formatter, then paste, type, or drop a file — it formats and validates as you go, with Repair, Minify, Expand, and the "About this JSON" panel. Open Settings to pick your theme and default view. PRIVACY This extension does not collect, store, or transmit any data. All formatting happens locally in your browser. It requests only the permissions needed to read the JSON on the page you are viewing and to save your settings.