How can I write useful alternative text for diagrams in a slide deck?

Start with the diagram’s purpose: what should someone understand from it? Then describe only the parts and relationships needed to grasp that purpose. Microsoft recommends concise, unambiguous PowerPoint alt text that conveys a visual’s intent and important content; for a diagram, it emphasizes purpose and relationships. It also advises not repeating nearby text. [S1]

A useful drafting prompt is: “This diagram shows [purpose]. [Key part A] connects to, leads to, or depends on [key part B], so [important takeaway].” Choose the relationship word that matches what the diagram actually depicts. If the slide title or nearby text already states the takeaway, don’t copy it into the description; add what someone needs to understand the visual itself.

Consider this hypothetical diagram: three boxes—“Request,” “Review,” and “Decision”—with arrows from Request to Review, then Review to Decision. Assume the slide explains the order of a process. A draft might be:

“Three connected boxes show a process: a request goes to review, then to a decision.”

That gives the purpose and sequence without listing box colors, positions, or decorative details. If the diagram instead had several review routes that changed the outcome, the description would need to explain those meaningful branches. Don’t compress a complicated relationship into a vague phrase such as “process diagram”; keep the distinctions that carry the point.

Use this worksheet:

1. Purpose: What does the diagram explain?
2. Essential parts: Which labels or components matter to that explanation?
3. Relationships: How do those parts connect, differ, or lead to one another?
4. Draft: Write one or two plain-language sentences using those answers.
5. Trim: Remove decorative details and anything already stated nearby, then check that the main relationship remains clear.

First decide which labels and paths are necessary to understand the diagram’s main point. Grouping details in your draft can help, but don’t collapse distinct routes if their differences matter. For example, if one route goes from “Review” to “Approve” and another goes to “Revise,” describe both routes and what distinguishes them; don’t merely say that the diagram has two arrows.

If the diagram has too many essential relationships to explain clearly in a concise description, consider whether the slide itself can be simplified or whether surrounding slide text can explain part of the content. Keep the description focused on the visual’s purpose and important content, not on a complete inventory of every mark. This is a writing aid, not a guarantee that one description will meet every audience’s needs; ask a reader to review it when the relationships are especially complex.

Check the instructions for the presentation app and version you use, then locate the diagram’s alternative-text option and enter your description there. Microsoft’s PowerPoint guidance covers visuals including shapes and SmartArt, and describes adding alt text and using the Accessibility Checker to find missing descriptions. Features can vary by version, and the guidance does not establish that every diagram type behaves identically in every presentation app. [S1]

After adding the text, review the slide in context: compare it with the visible diagram and nearby wording. Ask: Does the description identify the diagram’s purpose? Does it state the important connection or sequence? Does it avoid repeating the slide’s text? In PowerPoint, the Accessibility Checker can help find missing descriptions, but finding a missing description is not the same as judging whether your wording explains the diagram well. [S1]

Copyable draft: “[Diagram purpose]. [Key component or step] [relationship] [other component or step]. [Include a distinguishing branch or takeaway only if needed].”