Check alt text you already have

Quite a lot, as it turns out, and all of it is the sort of thing that survives a careful proofread. Alt text is invisible in a browser. It is not spell-checked by the CMS, it is not reviewed by the designer, and the person who wrote it has almost never heard it read aloud. So the failures that persist are not failures of care — they are failures nobody is in a position to notice.

The checks here divide into three. Some are about what a screen reader adds by itself: the element announces its own role before your text, so an opening that names the image again is heard twice. Some are about how a string is spoken rather than seen: a run of capitals is spelled out by several configurations, a missing full stop removes the pause before the next sentence, a comma-separated list is read as a list. And some are about what the attribute is for at all — a file name, a placeholder, or a description on an image that should have been announced as nothing.

Sentence case, the terminal full stop and the character guideline are conventions, and the checker grades them as conventions. It is entirely reasonable to ship alt text with no full stop, and it is entirely reasonable to run to two hundred characters when the picture is a chart. What is not reasonable is doing either by accident, which is the whole argument for saying it out loud and giving it the lowest weight there is.

The 125-character figure is the one most often quoted as though it were law. It appears in no success criterion. It comes from what older screen-reader configurations would read before breaking, and it is a good default for the same reason most defaults are good: it is right more often than it is wrong. The page on length sets out where it came from and which cases are allowed to ignore it.

• Whether the description is true. There is no image on this page — only the string you pasted — so a beautifully constructed sentence about the wrong photograph gets an A. The checker measures the shape of the writing, and the shape of the writing is not the same question as whether it matches the picture.
• Whether the image needed alt text at all. That decision belongs to the page the image sits on: the same photograph is informative next to a paragraph that refers to it and decorative next to one that does not. The decorative switch lets you tell the checker which case you are in; it cannot work that out on its own, and a tool that guessed would be guessing about your page rather than about your string.

Can I check a whole page of images at once?

Not here, and not yet. This route takes one string at a time on purpose — the findings are meant to be read and argued with rather than exported, and a list of two hundred graded rows is a spreadsheet nobody opens twice. A batch surface is planned and is honest about being planned; it is not hiding behind a disabled button.

What does the grade actually add up from?

A hundred points, minus forty-five for anything that stops the image working, eighteen for anything that costs the listener time, and six for a convention. A is ninety and above, E is under forty-five. The numbers are a presentation of the findings and nothing else, so if you disagree with a finding you should disagree with the grade too.

It flagged my alt text and I still think it is right. Now what?

Then it is probably right. Three of the checks here are conventions rather than rules — sentence case, the terminal full stop, the 125-character guideline — and a note is exactly what a convention deserves. The three graded as blockers are a different matter: a file name, a placeholder word and a missing alternative are not stylistic disagreements.

Does it check whether the description is accurate?

It cannot. There is no picture on this route at all — you are pasting a string and getting a reading of the string. Accuracy is the one thing that needs eyes on the image, and it stays a human job here.

• Alt textWrite the alt attribute yourself, with the picture open and the findings live.
• How long alt text should beWhere 125 characters came from, and the cases that are allowed to break it.
• When the right alt text is noneThe images that want an empty attribute, and why describing them is worse.
• WCAG 1.1.1 and GIGW, in plain termsWhat the success criterion asks for and what an Indian government audit checks.