To write good alt text, describe the image's purpose in a specific, concise sentence a screen reader can read aloud: what the image shows and why it matters in context. Keep it under roughly 125 characters, skip phrases like "image of" or "photo of," and mark purely decorative images with an empty alt="" so they're ignored. If the image is a link or button, describe where it goes, not what it looks like. Learning how to write alt text well is one of the highest-value accessibility fixes you can make, because missing image descriptions are among the most common WCAG failures on the web.
Why does alt text matter so much?
Alt text is the text alternative a screen reader announces when it reaches an image, and it's what search engines and AI systems read too. When it's missing or useless, a blind or low-vision visitor gets silence or a filename read letter by letter.
This isn't a rare edge case. In WebAIM's 2025 analysis of the top one million homepages, 94.8% had detectable WCAG failures, and missing image alt text ranked among the four most common problems alongside low-contrast text, missing form labels, and empty links. Scanners catch it reliably, so it shows up fast in an audit and fast in a plaintiff's demand letter.
Alt text maps directly to WCAG 2.2 Success Criterion 1.1.1 (Non-text Content), a Level A requirement — the minimum bar. Get it wrong and you fail the easiest level of the standard courts and regulators reference.
How do I write good alt text for images?
Start with one question: why is this image here? The same photo needs different alt text on different pages depending on what it's communicating.
Describe purpose, not pixels
Don't inventory every visual detail. Capture the point the image is making in context.
- Weak: "Woman with brown hair sitting at a wooden desk near a window smiling at a silver laptop."
- Strong: "Support agent taking a customer call."
The strong version tells the listener what the image contributes. Aim for the level of detail a sighted user absorbs in a glance.
Keep it concise
A practical ceiling is about 125 characters. Long alt attributes are a signal you're narrating instead of summarizing. If an image genuinely needs a paragraph — a complex diagram or infographic — put that description in the visible page text or a caption, and keep the alt short.
Skip redundant phrases
Screen readers already announce that an element is an image. Writing "image of a golden retriever" makes the software say "image, image of a golden retriever." Just write "Golden retriever." Drop "picture of," "photo of," and "graphic of."
Don't keyword-stuff
Alt text does help SEO, but cramming keywords in produces text that's useless to actual screen-reader users and reads as spam to search engines. Write for the human listening first; the SEO benefit follows naturally from honest, descriptive text.
What alt text should decorative images have?
Not every image carries information. Background textures, spacer graphics, and photos that only repeat what nearby text already says are decorative. For these, use an explicitly empty alt attribute: alt="".
An empty alt tells the screen reader to skip the image entirely. This is very different from omitting the alt attribute — when alt is missing, many screen readers read the filename aloud, so a visitor hears "D-S-C underscore zero four nine two dot J-P-G." Empty and absent are not the same thing.
Rule of thumb: if removing the image would lose no meaning for a sighted reader, it's decorative. If a caption or adjacent sentence already conveys the point, the image is decorative too.
How do I write alt text for links, buttons, and logos?
When an image is functional — it's inside a link or acts as a button — the alt text must describe the destination or action, not the artwork.
Image links
A logo in the header that links home should read alt="ADA Fail home", not "ADA Fail logo." The listener needs to know the link's function. A magnifying-glass icon that submits a search should be alt="Search".
Buttons and icons
Icon-only buttons are a frequent audit failure — they surface as "empty links" or "empty buttons," another of WebAIM's top failure types. Every icon that does something needs an accessible name, via alt text, an aria-label, or visually hidden text.
How do I write alt text for charts and infographics?
Data images are where short alt text isn't enough. A screen-reader user deserves the same insight a sighted reader gets from the chart, not "bar chart." Give the chart a short alt that states its topic and takeaway — alt="Bar chart: web-accessibility lawsuits rose about 20% in 2025" — and then provide the underlying numbers in the page itself, as a real HTML table or a text summary below the image. The full data belongs in the document, where everyone can reach it and where it also becomes indexable content.
The same logic covers infographics. If you'd struggle to summarize the image in a sentence, that's a sign the information shouldn't be locked inside a picture at all.
How do I check my alt text against a real audit?
Automated tools will flag the obvious problems — missing alt attributes, empty functional links — and fixing those is genuine progress. But remember that automated scanning detects only about a third of WCAG success criteria. A scanner can tell you an image has alt text; it can't tell you the alt text is accurate. "image123" as alt passes the presence check and fails a human reviewer instantly.
Run through this quickly on any page:
- Every informative image has specific, purposeful alt text.
- Every decorative image has alt="" (empty, not missing).
- Every image link or button describes its destination or action.
- No alt text starts with "image of" or "photo of."
- Charts and infographics have their data available as page text.
That's the difference between passing automated scans and genuinely working for people who rely on assistive technology. Our free accessibility audit checks alt text against WCAG 2.2 AA and flags the ones a scanner would wave through.
Alt text is one item on a longer list. If you're still running a third-party overlay you believe is covering this for you, read why overlay widgets fail — they routinely leave exactly these image problems unfixed.
Frequently asked questions
Does alt text have a character limit?
There's no hard technical limit, but a practical target is around 125 characters. Some older screen-reader-and-browser combinations truncate very long alt attributes, and long alt text usually means you're narrating detail that belongs in visible page copy or a caption instead. Keep alt short and purposeful; move complex descriptions into the document body where every reader can access them.
Is missing alt text enough to get a website sued?
No single missing description triggers a lawsuit, but image problems are frequently cited in demand letters because they're easy for a plaintiff's tester to document with a free scan. Missing alt text is a Level A failure — the minimum conformance level — and widespread missing or junk alt text is a visible, provable barrier. Our overview of how serial plaintiffs pick targets explains why low-effort, high-count failures attract attention.
Can an accessibility widget or overlay write alt text for me?
Not reliably, and not in a way that passes real human review. Some overlays auto-generate alt text with AI, but the results are frequently vague, wrong, or context-blind — a decorative image gets described, a functional icon gets the wrong action. A user-facing preference widget (letting visitors adjust contrast or text size on a site that's already accessible in its code) is a legitimate convenience that makes no compliance claims. A third-party compliance overlay that promises to fix your images automatically is a different thing entirely: the FTC's 2025 action against accessiBe centered on exactly these kinds of unsubstantiated claims. See our comparison of an accessibility widget versus an overlay for the full distinction.
Good alt text is one of the fastest, cheapest accessibility wins available — and one of the first things any auditor or plaintiff checks. To find out which of your images pass and which would fail a human reviewer, start with a free accessibility audit from ADA Fail. We'll show you exactly what to fix and how.