OneTaskBy Tim King · Updated
Annotate Screenshot Online
Arrows, Boxes, Numbers, Blur and Pixelate, Free
OneTask is free, with no sign-up, and built by one person.
If this tool saved you time, a coffee helps keep new ones coming.
How the Image Annotator works
Use this to annotate screenshot online with arrows, boxes and text. Add a screenshot — or paste-drop one onto the canvas — and it becomes the picture at full size. Arrow, Box and Circle drop red shapes in the middle to drag into place; Number adds the next numbered marker for step-by-step guides; Highlight is a translucent yellow bar; Add text is a label. To hide an email address or a face, draw a Box over it and press Pixelate area or Blur area, and the box is replaced by the obscured pixels. Crop to box trims the whole picture to a box. Download PNG saves the result.
Annotate screenshot online: what to know first
A bug report, a how-to, a "which button do I press" message to a relative — they all need a screenshot with an arrow on it, and doing that in an image editor is more steps than it should be. This page is the minimum: the picture, a row of marks, and a download. It runs in the browser, so the screenshot never leaves your machine, which matters when it has your inbox or your bank balance in it.
The marks. Arrows are a line and a head grouped together, so they rotate and stretch as one; boxes and circles are outlines with no fill so they frame a thing without hiding it; the numbered markers count up from one each time you press Number, so a set of instructions gets 1, 2, 3 in order. Click any mark to change its colour, outline width or opacity in the Selected item panel. Marker colour and Line width in the side panel set the defaults for new marks.
Hiding things. Pixelate and Blur work on a region you have marked: draw a Box or Circle over the area, keep it selected, and press the button. The tool copies the pixels under the box's bounding rectangle, runs a pixelate or blur filter over them, and puts the result back as a new layer in place of the box. It is real destruction of the detail, not an overlay — the output PNG has only the coarse blocks. A very small area gets small blocks, a large one gets large; for a guaranteed opaque redaction use a filled Box instead, or the image redactor.
Cropping. Draw a Box around the part you want to keep and press Crop to box. The canvas shrinks to that rectangle and every mark you have already added moves with it, so you can mark first and crop afterwards.
Resolution. The canvas takes the size of the screenshot, capped at 2400 pixels wide, and is shown scaled to fit. Line widths and marker sizes are in pixels of the original, so they stay proportionate on a 4K capture and on a phone screenshot alike. Download PNG exports at full size.
Privacy. The image is opened by the page from your disk and drawn to a canvas element. There is no upload, no server-side processing, and the download is generated locally.
FAQ
Is the blurred area recoverable?
Blur less than pixelate: heavy blur removes small text reliably, but a light blur on large text can sometimes be guessed at. Pixelate with the default block size is not reversible in practice. For anything sensitive, a solid filled box is the safe choice.
Can I annotate a PDF page?
Not directly. Take a screenshot of the page at the zoom level you want, or export the page as an image from your PDF viewer, then add the result here and mark it up as usual.
How do I change the arrow direction?
Click it and drag the rotation handle above the selection box, or just drag the whole arrow and rotate it to point where you need. Corner handles stretch it longer.
Why does the Number button start at 1 again?
The count resets when you press Reset. If you delete marker 3 and add a new one it will be 4, since the counter does not go back; edit the number by double-clicking it if you need a specific value.
Does this work on a phone?
Yes. Add image opens the photo library or camera, and the marks can be dragged with a finger. Fine positioning is easier with a mouse.
See also: all Images tools, Audio, Video & Screen, PDF, SVG, Simulations & Screensavers, Generative Art, Chart Makers, 3D Model Viewers, Drawing Pads, Mockups & 3D Making, Diagram Makers, 3D Science, Tracker Music.
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