Alt Text Guide: Accessibility, SEO & What to Describe
Accessibility6 min readMay 2026
Alt text is the easiest accessibility win you can make — a single attribute that opens your content to millions of screen reader users and earns image-search visibility. Done well, it takes 30 seconds per image. Done badly, it's worse than nothing.
Alt Text Decision Table
Image Type
Alt Text Approach
Example
Decorative
Empty alt=""
Background patterns, dividers
Functional (link/button)
Describe the action
"Search" not "magnifying glass"
Informative
Describe key meaning
"Red warning triangle: backup failed"
Complex (chart)
Summarize finding + link to long desc
"Bar chart: 65% chose dark mode"
Text in image
Transcribe the text
"50% off — ends Sunday"
What to Describe
Describe what's relevant in context, not the photograph in detail. A picture of a chef next to a recipe needs "Chef plating finished pasta" — not "smiling man in white jacket with arms raised holding tongs over a white plate next to a blue tile counter." Context determines relevance.
Rules That Always Apply
Skip "image of" or "picture of" — screen readers already announce it as an image.
End with a period so screen readers pause before the next element.
Match the context — same image may need different alt text on different pages.
Don't keyword stuff. One natural keyword maximum.
Always set the attribute — empty alt="" is valid; missing alt is not.
Common Mistakes
Leaving the filename as alt text ("IMG_2034.jpg").
Marking informative images as decorative to skip them.
Writing "icon" or "logo" instead of the brand/action.
Repeating the visible caption verbatim.
Stuffing keywords for SEO and hurting clarity.
Check Your Page Copy
Make sure surrounding text reads naturally for screen readers too.
Alt text is a textual replacement for an image. It is read aloud by screen readers, shown when images fail to load, used by search engines to understand the image, and parsed by AI agents reading the page. It is not a caption (visible text under the image), not a tooltip (hover text), and not a place for SEO keyword stuffing. The single test: if you remove the image and replace it with the alt text, does the page still make sense? If yes, the alt text is doing its job.
Four patterns that cover almost every image
Informative images (a photo of a product, a diagram) — describe the content concisely. "A red Patagonia Down Sweater jacket on a white background, three-quarter view."
Functional images (a logo that links home, a search icon button) — describe the function, not the visual. alt="Home" for the logo link, alt="Search" for the magnifier.
Decorative images (a stock photo banner, a separator) — use empty alt: alt="". This tells screen readers to skip. Do not omit the attribute — screen readers may then read the filename aloud.
Complex images (charts, infographics) — short alt summarises ("Bar chart of revenue by quarter, 2023") with the full data described nearby in the text or via aria-describedby.
Common mistakes
Starting with "Image of…" or "Picture of…" — screen readers already announce "image". The prefix wastes time.
Stuffing keywords. Google penalises this and it ruins the experience for screen-reader users.
Reusing the same alt text on every image. Especially common with product galleries where every angle is labelled "Patagonia Down Sweater". Differentiate: "front view", "side detail", "hood up".
Long alt for decorative images. If the image adds no information, give it empty alt and move on.
Missing alt attributes entirely. WCAG 1.1.1 failure, and a hard blocker for accessibility audits.
Length and style
Aim for 125 characters or fewer — many screen readers cut off there or pause awkwardly. Use sentence case with punctuation. Skip articles only if it saves space and reads naturally ("Logo, SarvKit" is fine; "The SarvKit company logo, in blue and white" is better).
Test by listening. Open VoiceOver (Mac), NVDA (Windows, free), or TalkBack (Android) and navigate a page. The places where you cringe at what is read aloud are the places where the alt text needs work.
Frequently Asked Questions
Accessibility for screen readers, graceful fallback, and modest SEO benefit.
Usually 80-125 characters. Use captions or long descriptions for more.
Use alt="" for decorative images. Never omit the attribute.
State the takeaway first, then key data. Link to a long description if needed.
Yes — especially for image search. Write naturally, don't stuff keywords.