Alt text is one of those details that is easy to skip under deadline pressure, invisible in the normal browsing experience, and consequently one of the most commonly neglected pieces of on-page SEO and accessibility work — yet it directly serves two real audiences: people using screen readers who cannot see the image at all, and search engines that cannot "see" an image in any meaningful sense either and rely entirely on the alt text to understand what it depicts. Getting alt text right serves both audiences at once with the same piece of writing.
What alt text actually does
Alt text (the HTML alt attribute on an image tag) is a short text description that stands in for the image whenever the image itself cannot be conveyed — read aloud by a screen reader for a visually impaired user, displayed as fallback text if the image fails to load, and parsed by search engine crawlers that index the surrounding page content, including image search results, based partly on what the alt text says the image contains. Every one of these three uses depends on the alt text actually, accurately describing what is in the image — a missing or generic alt text fails all three simultaneously.
What makes alt text genuinely good
Good alt text is specific, concise, and describes what is relevant about the image in its context — not necessarily every visual detail, but what a sighted user would take away from glancing at it. "Woman using a laptop" is technically accurate but nearly useless if the image is actually illustrating a specific product feature; "Woman comparing two spreadsheet columns side by side on a laptop screen" conveys the actual point the image is making. Context matters enormously: the same photograph might warrant different alt text depending on whether it illustrates a blog post about remote work, a product page for a laptop, or a stock photography listing — write for what the image is doing on this specific page, not a generic description that could apply anywhere.
Common alt text mistakes
A handful of patterns show up repeatedly and undermine alt text's usefulness. Leaving it blank entirely is the most basic failure, offering nothing to either screen readers or search engines. Keyword stuffing — cramming multiple target keywords into an alt attribute that no longer reads as a natural description ("shoes running shoes buy running shoes online cheap") — is both unhelpful to actual users and increasingly recognised and penalised by search engines as a manipulative pattern rather than genuine optimisation. Redundant phrases like "image of" or "picture of" add no value, since screen readers already announce that the content is an image before reading the alt text — the phrase is simply wasted words that make the description less concise. Generic filler like "photo1234.jpg" or "banner image" describes nothing at all and might as well be blank.
When alt text should be empty on purpose
Not every image needs descriptive alt text — purely decorative images that add no informational content (a repeating background pattern, a decorative divider line, an icon that duplicates adjacent text) should have an empty alt attribute (alt=""), which correctly signals to screen readers to skip announcing the image entirely rather than interrupting the reading flow with a description of something that carries no meaning. This is different from omitting the alt attribute altogether, which some screen readers handle by reading out the image filename instead — genuinely worse than silence for a decorative image. Knowing when to write a description versus when to deliberately leave it empty is itself part of writing alt text well.
Alt text vs image titles and captions
Alt text is sometimes confused with the image title attribute (shown as a hover tooltip on most browsers) or a visible caption displayed beneath the image — these serve different purposes and are not interchangeable. Alt text is specifically for accessibility and search engines, and should be present on every meaningful image regardless of whether a visible caption also exists; a caption can add supplementary context or attribution visible to sighted users, but it does not substitute for alt text, since a screen reader treats them as separate pieces of information serving different roles.
Checking alt text across an entire site
Writing good alt text one image at a time is straightforward, but auditing an existing site with hundreds or thousands of images for missing or poor alt text by hand is impractical — the Alt Text Bulk Checker scans a page (or a batch of URLs) and flags images with missing, empty, or suspiciously generic alt attributes, turning what would be a tedious manual review into a quick audit you can act on systematically. Running this kind of check periodically, especially after a content migration or a redesign (both common times for alt text to get silently dropped), catches regressions before they accumulate across the whole site.
Don't forget the favicon and other small images
While alt text is the main accessibility and SEO concern for content images, small branding elements like a site's favicon also contribute to how a page is perceived and recognised across browser tabs and bookmarks, and it is worth periodically confirming these render correctly across platforms — the Favicon Preview Checker shows how a favicon appears at the various sizes different browsers and devices actually use, catching a favicon that looks fine at one size but blurs or disappears at another. And since alt text sits alongside the broader question of how thoroughly a page communicates its content, pairing an alt-text audit with a check via the Content Length Analyzer gives a fuller picture of a page's overall completeness.
Key takeaways
- Alt text serves screen reader users, broken-image fallback display, and search engines — all from the same description.
- Write specific, contextual descriptions of what matters about the image on that particular page — avoid keyword stuffing and "image of" filler.
- Purely decorative images should have an empty alt="" attribute, not a missing one or a forced description.
- Audit alt text across a whole site periodically, especially after migrations or redesigns, since it silently gets dropped often.