How to write alt text: a practical guide with examples

Alt text (alternative text) is a short written description of an image that screen readers read aloud in place of the image. Good alt text gives people who can't see the image the same information or purpose it gives everyone else, in as few words as it takes. Images that add nothing should be marked as decorative so screen readers skip them. WCAG sets no character limit, but most good alt text is a phrase or a sentence or two.

Start with why the image is there

The most common mistake is describing what an image looks like instead of what it's for. Before you write anything, ask two questions:

• Why did the author put this image here?
• If I were reading this document to someone over the phone, what would I say about the image?

The same photo can need different alt text in different documents. Take a photo of a new branch library:

• In a news release about the opening: "The new Eastside Branch Library, a two-story brick building with a glass entrance."
• In a report on energy savings: "Solar panels covering the south roof of the Eastside Branch Library."
• On a page of library hours, right under the heading "Eastside Branch": mark it as decorative. It adds nothing the heading doesn't already say.

Context decides. That's why alt text is one of the things software can draft but a person has to confirm.

A five-question decision process

This follows the W3C's alt text decision tree (linked in the sources below), which is worth bookmarking for the cases that don't fit neatly.

Alt text best practices

• Lead with what matters. Put the key information first. People using a screen reader can move on as soon as they have what they need.
• Skip "image of" and "picture of". Screen readers already announce that it's an image. Name the type only when it matters, such as "Screenshot of the permit portal" or "1920s photo of the courthouse".
• Be specific. "Crew repaving Main Street" says more than "Road work".
• Don't repeat the caption. If a caption or the next sentence already explains the image, keep the alt text short or mark the image decorative, so people don't hear the same thing twice.
• Include any text that's in the image. If a flyer image says "Public hearing, March 9, 6 p.m.", so must the alt text. Better still, put those words in the document as real text.
• Keep it short, but complete. There's no character limit in WCAG. If you find yourself writing a paragraph, the information probably belongs in the body text or a long description that everyone can read.
• Write in the document's language and use normal punctuation, so screen readers pause in the right places. Spell out abbreviations your readers may not know.
• Describe people only as far as it matters. Use names if the document names the person and it's relevant. Don't guess at anyone's age, race, gender or disability.
• Never use the file name. "IMG_4482.jpg" or "Picture 3" is worse than nothing, because people have to sit through it.

Decorative images

An image is decorative when removing it would lose no information. Common examples are page borders, background shapes, divider lines, stock photos used only for mood, and icons that sit next to text saying the same thing.

Mark decorative images so assistive technology skips them:

• Word, PowerPoint and Excel (Microsoft 365): open the Alt Text pane and check Mark as decorative.
• PDF: a decorative image should be an artifact, not a Figure tag. In Adobe Acrobat Pro, check Decorative figure in the Set Alternate Text dialog, or right-click the image in the Content panel and choose Create Artifact. You can also mark it as background in the Reading Order tool.
• Canvas and most web editors: check the decorative option in the image settings.

In a PDF, don't leave a Figure tag with empty alt text. Checkers flag it, and some screen readers announce an unlabeled graphic. If it's decoration, make it an artifact. Our guide to tagged PDFs explains artifacts in more detail.

Special cases

Logos and seals. If the organization's name is already in the heading beside the logo, mark the logo as decorative. If it stands alone, use the name, such as "Example County seal". If the logo is a link, describe the link: "Example County home page".

Signatures. People need to know that a document was signed and by whom, not what the signature looks like. If the signer's name is typed below it, "Signature" is enough. If not, include the name and role: "Signature of [name], Board Secretary".

Text in images. Scanned notices, quote graphics and flyers saved as pictures need alt text that includes all the words that matter. For more than a sentence or two, replace the image with real text. WCAG 2.1 AA asks you to use real text instead of images of text wherever you can (1.4.5 Images of Text). Whole scanned pages need OCR; see scanned PDFs and OCR.

Charts, graphs and maps. Use short alt text that names the image and gives the main point, plus the full data or directions somewhere people can read them. Our alt text for charts and graphs guide has examples and Excel steps.

Icons. An icon next to a word that says the same thing is decorative. An icon used on its own needs alt text for its meaning: a phone icon before a number is "Phone", and a warning triangle is "Warning".

QR codes. Say where the code goes: "QR code for the parks survey". Always print the web address as text as well, because many people can't scan a code.

Screenshots in instructions. Describe what the reader needs in order to act, not every detail on screen.

Math. A formula needs alt text that reads it aloud, such as "x equals negative b plus or minus the square root of b squared minus 4 a c, all over 2 a".

Alt text examples: weak vs. better

Where to add alt text

Adding alt text in the source file is best: Word and PowerPoint carry it into the PDF when you export with accessibility tags turned on. Step-by-step help for each app is in our Word, PowerPoint and Excel guides, and our main guide on how to make a PDF accessible covers PDFs.

Check your alt text

• Read it without the images. Go through the alt text in order. Does the document still make sense?
• Listen to it. Use a screen reader such as NVDA (free for Windows) or VoiceOver (built into Macs and iPhones), or the screen reader preview in the free PAC checker.
• Don't rely on a checker's green tick. Acrobat's "Figures alternate text" rule only confirms that alt text exists, and Microsoft's Accessibility Checker adds only a check for file names. Alt text that says "image" passes both. See what the Microsoft checker doesn't check.

Fix it automatically

Includoc's AI drafts alt text for every image in a PDF, Word, PowerPoint or Excel file. It looks at the image, the text around it and the document's title, suggests which images are decorative, and flags charts that need a longer description. A person then approves or edits each one, because only someone who knows why the image is there can confirm what it means. For a single image, try our free alt text generator.

Standards

Sources

• W3C: Understanding Success Criterion 1.1.1 Non-text Content (opens another website)
• W3C: Understanding Success Criterion 1.4.5 Images of Text (opens another website)
• W3C Web Accessibility Initiative: Images tutorial (opens another website) and An alt decision tree (opens another website)
• W3C: PDF1: Applying text alternatives to images with the Alt entry in PDF documents (opens another website)
• W3C: PDF4: Hiding decorative images with the Artifact tag in PDF documents (opens another website)
• Microsoft: Everything you need to know to write effective alt text (opens another website)
• Adobe: Create and verify PDF accessibility (Acrobat Pro) (opens another website)