How to annotate a screenshot on a Mac: arrows, steps and blur

A screenshot on its own makes the reader do the work. They have to find the button, guess which field you mean and wonder what you want them to do. If you want to annotate a screenshot on a Mac so that it lands the first time, you need three marks: an arrow, a step number and a blur. That is nearly all of it.

Start with one arrow

Most screenshots have one thing that matters and forty things that do not. An arrow tells the reader where to look before they start reading.

In catu, take the screenshot with ⇧⌘2, then click the preview on the card that slides in, or press Edit. The editor opens with Arrow already selected, in red. Drag from the tail to the point. Hold ⇧ and it snaps to horizontal, vertical or 45°, which looks tidier than a wobbly diagonal.

Keep it to one arrow per idea. Two arrows pointing at two things is a list, and a list wants numbers. If the thing is small, say a tiny toggle in a crowded toolbar, use Magnifier (M) instead. Drag over the detail and catu places an enlarged copy beside it, joined by a line.

A designer sending a review does not need a paragraph. A screenshot, one arrow and one line of text that says "this gap should be 16" is enough.

Number the steps, don't describe them

"Click the gear, then the third item down, then the blue button" is slow to read and easy to get wrong. Numbers are faster.

Press N for Step number and click where each step happens. Each click adds the next number: 1, 2, 3. The reader follows them in order without being told to.

This is how a teacher explains one step, or how a developer shows where a bug appears. The screenshot becomes the instructions. You write almost nothing under it.

Two small habits help:

• Place the number beside the thing, not on top of it, so the button stays visible.
• Stop at five or six. If you need more, it is two screenshots.

When you need words, use Text (T). It is bold with a thin white outline, so it reads on any background. Text cannot be retyped once placed. Remove it and add it again.

Hide what is private

Before a screenshot leaves your Mac, look for email addresses, account numbers, names and anything that looks like a password. Hiding them takes ten seconds.

catu has three tools for it. Pixelate (X) covers an area in large blocks. Hide text only (D) finds the lines of text inside the area you drag over and pixelates only those, so icons and layout stay visible. Blur (B) softens an area.

Our advice is to use Pixelate or Hide text only for anything sensitive. As the help centre puts it, their blocks are too coarse to read back. A blur looks softer but can sometimes be partly undone. If catu shows "No text found there", drag over a larger area or switch to Pixelate.

There is also Remove object (E), which fills an area from its surroundings. It works best on plain backgrounds, such as taking a notification badge out of a toolbar.

Make the important part the loudest

The last move is subtraction. Two tools do it.

Spotlight (S) dims everything except the area you drag over. Add several to light up more than one place. Crop (C) removes what is not needed: drag the area to keep, then press Return.

A cropped, spotlit screenshot with one arrow beats a full-screen capture with six marks. Crop first if you can. The reader sees less, so they understand more.

If you want a before and after, use Combine with another screenshot on the right of the toolbar. It adds a second image below or to the right. Combine first, then crop, because combining undoes any crop.

Your marks stay editable until you copy or save, so you can change a colour or move an arrow with Select (V) at any point. Colour is one click. The eight choices run from red to white, and the line width is Thin, Medium or Thick.

Try this today

Take the next screenshot you were going to send as it is, and spend one minute on it:

1. Press ⇧⌘2 and capture only the part that matters.
2. Click the preview to open the editor.
3. Add one arrow, or numbers if there are steps.
4. Hide anything private with Hide text only.
5. Press Return. The edited image is copied and the editor closes. Paste it with ⌘V.

One thing to remember: Esc and ⌘W close the editor without copying or saving, and there is no warning. Copy or save first.

What catu does about it

All of these tools are in catu's editor on the Mac, and they are free. Your screenshot stays on your Mac, marks and all, until you choose to share it. There is a full list of tools and keys in Mark up a screenshot.