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Glossary

Alt text

Alt text is the short description of an image written in its alt attribute. Screen readers read it aloud, browsers show it when the image does not load, and search engines use it to understand what the image shows.

Also called alt attribute, alternative text.

By NightshiftDirect Research. Published . Updated .

Why images need words

The accessibility tutorial from the W3C, the body that sets web standards, starts from one rule: images must have text alternatives that describe the information or the function they carry (W3C WAI). A visitor who cannot see your photos gets the words instead. The tutorial draws on the Web Content Accessibility Guidelines, including success criterion 1.1.1, Non-text Content.

Not every image has something to say. When a picture is on the page only to decorate it, the tutorial's answer is a null text alternative, written alt="" (W3C WAI). The attribute is there, and it is empty on purpose.

How Google uses it

Google calls alt text the most important attribute for giving it information about an image. It reads the alt text together with what computer vision finds in the picture and what the page around it says (Google Search Central).

Google makes the same case the W3C does: alt text helps people who cannot see images, including screen reader users and people on slow connections. It also warns against filling alt attributes with keywords, which makes for a poor experience and may make your site look like spam (Google Search Central).

What to write for each kind of image

Decide from the image's purpose, which is how the tutorial sorts them (W3C WAI). A photo of your work carries information, so say what it shows: a technician fitting a water heater, or a finished slate roof.

A logo or icon that works as a link is described by what the link does, so a logo that takes visitors home reads as your business name and the word home. An image that contains words, such as a banner reading "Free estimates", repeats those words. A background texture or a divider line gets alt="".

Linking an image gives its alt text a second job. Google treats the alt attribute of a linked image as its anchor text, the words that tell people and Google what the linked page is about (Google Search Central). A button made from an image that reads "Book a service call" needs those same words in its alt text, or the link has no anchor text for Google.

What to leave out

Keyword lists. An alt text reading "plumber plumbing emergency plumber drain repair" tells a listener nothing about the photo, and it is the stuffing Google warns about (Google Search Central). Openers such as "photo of" add words without adding meaning. Start with what the photo shows.

The same words on every photo. A gallery of project photos all described as "roof repair" gives a listener the same line over and over. Google asks for useful, information-rich alt text written in the context of the page (Google Search Central), and one description pasted across a whole gallery is neither.

How the scan checks it

The free scan counts the images on the pages it reads and how many of them have no alt attribute at all. Once it has read enough images to judge, and too many of them lack one, it reports E7 with the count. An image marked alt="" counts as described, so marking your decorations correctly will not set it off. It counts only images written into the HTML your server sends, so a gallery that a script fills in later is left out (what the scan reads).

What the free scan checks

Questions

Does my logo need alt text?

Yes. If your logo links to your home page, describe the link: your business name and the word home. If it is not a link, your business name is enough, because an image of words repeats the words (W3C WAI).

Should my alt text mention my town?

Only when it helps describe the photo in the context of the page, such as a finished job on a page about work in that town. Putting the town on every image to catch local searches repeats one keyword across every photo, and Google asks you not to fill alt text with keywords (Google Search Central).

Does every photo on my site need a description?

Every photo that tells the visitor something does, such as your finished work or your team at a job. A photo that is there only for looks, such as a stock background behind a heading, gets alt="" instead. If you are not sure which a photo is, ask whether the page would lose any information without it (W3C WAI).

Where this fits in our work

We handle this as part of Content: Service pages, local pages and articles that answer what your buyers ask, with every statistic linked to its source.

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