How do I write useful captions for diagrams in a task guide?

Start by asking what the reader needs to do with the diagram at this point in the guide. A title often names the subject—“Parts of the form,” for example. A useful caption adds the reader’s purpose: “Use the numbered labels to locate the fields described in step 2.”

A simple pattern is: “Use [feature of the diagram] to [reader’s purpose].” Other options include:

1. “The arrows show [direction or order], helping you [task].”
2. “Compare [part A] with [part B] to see [relevant difference].”
3. “The callouts identify [items] referred to in [step or section].”

Only describe what the diagram actually shows. If it doesn’t mark an order, don’t imply that it does. The caption should orient the reader; the task instructions should still explain what to do.

Choose the feature that matters most for the current step. Listing every visible detail can turn the caption into an inventory and hide the point. If readers need more than one feature, name their relationship: “Follow the arrows from the start marker to the two labeled choices.”

For example, suppose an imaginary guide includes a diagram of a sample worksheet with lettered sections and an arrow between two of them. A task-focused caption could be: “Use the letters to find the sections named in step 3; the arrow shows which section to check next.” This example assumes those letters and that arrow are actually present. If the guide gives step 3 a different purpose, revise the caption to match.

Keep names consistent. If the guide calls a part “Review box,” don’t call it “approval area” in the caption unless those terms mean the same thing and you explain that.

Look for any instruction that identifies something only by color, such as “choose the green section.” Add another visible cue: a label, symbol, pattern, position, or shape. For instance, if the diagram uses color to distinguish two routes, label them “Route A” and “Route B” and refer to those labels in the caption or steps. Use this only if the labels are actually added to the diagram.

Then check the caption on its own: does it tell readers what the marks refer to and what they help locate or understand? If a color distinction is essential, explain it in words and provide a non-color cue in the diagram. Don’t rely on the caption to resolve a distinction that the diagram itself leaves unclear.

Try this routine:

1. Identify the step or decision the diagram supports.
2. Pick the visual feature that helps with that task.
3. State what that feature helps the reader locate, follow, compare, or understand.
4. Check the caption against the diagram and nearby instructions; remove unsupported details or repeated wording.
5. Replace color-only references with labels or another visible cue, then check that the instructions still make sense.

Copyable template: “Use [label, arrow, shape, or other feature] to [locate/follow/compare] [specific item or relationship] for [task or step].”

Example with placeholders: “Use the [lettered labels] to locate the [sections] named in [step number].” Fill this in only with details that appear in your guide. A caption can orient the reader, but it cannot clarify a diagram whose symbols or relationships are ambiguous; revise the diagram or explain it in the task text as well.