Accessibility
Alt text is the accessibility failure with the widest reach and the simplest detection rule, which is why it is also the one most often fixed badly: a scanner passes, a reader is still lost.
In a markdown or HTML document, an image without an alt attribute is a mechanical finding: the tag is there and the description is not.
A second pattern is nearly as common and worse than absence: alt text that repeats the filename, the CMS ID or a stock photo caption of no use to anyone.
A third is a missing attribute where an empty one is correct. Decorative images should carry alt="", which a naive rule reports as missing.
The distinction decides the correct answer for every image, and it depends on context rather than on the file.
An informative image carries content a reader would otherwise miss: a diagram showing a flow, a screenshot of an error, a chart with a conclusion. It needs a description of what it conveys, not of what it contains.
A decorative image provides texture or spacing and conveys nothing: a divider, a shadow, a background flourish. It needs an empty alt attribute so assistive technology skips it rather than announcing it.
The same picture can be either, depending on placement. A logo in the header is decorative when the adjacent text says the company name and informative when it is the only identification.
Describe the function, not the medium. Not a blue bar chart but sign-ups rising sharply after March, if that is the point being made.
Keep it to a sentence for most images. For a complex diagram, describe the structure and the takeaway, and put the detail in the surrounding text rather than in a 300-character attribute.
Do not start with image of. Do not repeat the caption. If the caption already carries the meaning, the alt text can describe only what the caption does not.
Whether the description is accurate. A wrong alt text is worse than none, because it substitutes a false claim for a visible gap.
Whether the image is described at the right level of detail for the context. That depends on the audience and on what the page is arguing.
Whether the image should be there at all. Generated documents often include an illustrative picture that adds nothing, which the correct fix is to delete.
Put the check before publication rather than after an audit. A missing attribute takes seconds to add while drafting and a ticket to add afterwards.
Make the alt text part of the brief for generated content. If the prompt asks for descriptive alt text and the pipeline preserves it, most of the finding disappears.
Sample live pages quarterly. Templates and embeds reintroduce the problem, particularly where a CMS supplies an image with no description field filled in.
Beyond the moral case, alt text is the cheapest accessibility win available: a sentence per image, no design work, no code change.
It is also a legal exposure in several jurisdictions, where failure to provide a text alternative is a documented complaint pattern rather than a theoretical risk.
And it improves the page for everyone: the description is what a reader sees when the image fails to load on a bad connection.
Attribute present
Every image has an alt attribute, even if its value is empty.
Correct empty alts
Decorative images marked empty rather than given filler description.
No filename alts
Descriptions that add information rather than repeating a file name.
Function described
Informative images described by what they convey, not by their appearance.
Brief includes alt
Generated content asked for descriptions so the finding never appears.
More in Document and web: CSV validation tool, Markdown linter, Broken anchor checker, HTML markup checker, Website metadata audit, Broken link checker, Document QA workflow.
Missing alt text scanner
The automated pass is free, needs no account and uploads nothing. Escalate to a named reviewer only where being wrong is expensive.
