Sketch File Viewer

Sketch is a Mac app. A designer sends a landing page, a set of app screens or an icon grid as a .sketch file, and the person who has to look at it is on Windows, a Chromebook or a phone. Sketch itself does not run there. This page opens the file in the browser you already have, with nothing to install and no account. You see the preview the file shipped with, the page and artboard names, and the layer tree, then you can save a PNG to drop into a chat or a slide.

Since Sketch 43 the file has been a zip archive of JSON, which is why a modern .sketch opens without the app. At the top of the zip are document.json (shared colours, text styles and the list of pages) and meta.json (the app version and the page and artboard names). Each page is a JSON file under pages/. A small PNG of the canvas sits at previews/preview.png, and that is what you see first, before the layer tree is walked. The format is documented by Sketch for anyone building a reader, which is what this page is.

The layer tree is the part a screenshot cannot give you. Every layer keeps the name it had in Sketch, a plain type such as Artboard, Group, Rectangle, Text or Image, and a visible or hidden mark. Hidden layers stay in the list so you can see that a note or an old draft is in the file even though it is not on the preview. Text layers are collected into Copy text, one layer after another, so a headline or a button label can be pasted into a doc without retyping it. Files with several pages list every page and the artboards on it.

Two PNG buttons do different jobs. Download PNG saves the embedded preview, the same picture Sketch wrote into the file, so it matches what the designer saw when they saved. Save artboard as PNG draws that artboard from its rectangles, ovals and text. It is a simple drawing, not a full Sketch render: images, symbols, blurs and boolean shapes are not painted, and text uses a plain font, so the PNG can differ from the app. The page says so. When a file has no preview image at all, the same simple drawing is shown on screen and labelled approximate.

Design files often contain unreleased product screens, real names in a prototype, or copy that is not public yet. This page does not upload the file. It is unzipped and read by code in this tab, the preview is drawn from bytes that were already inside the zip, and the PNG you download is made on your device. TaskNinja never receives the file, and it is not sent to an AI model. Close the tab and the working copy is gone.

A few files are refused on purpose, with a plain message rather than a blank page. The name has to end in .sketch. A zip that is some other archive, missing document.json or meta.json, is not treated as Sketch. An empty file, a damaged zip, and a Sketch file from before Sketch 43 (those used a private binary, not JSON) each get their own reason. A file that is a real Sketch document but has no preview still opens: you get the layer tree and, when the layers are simple shapes or text, an approximate picture.