Test if a website defines text alternatives for images, audio and video
Why is it important?
Not including alternative text means that search engines and users with visual impairments are unable to identify that content. This is particularly important where an image contains text that is unavailable elsewhere, such as a phone number or company name.
Including alternative text is one of the most crucial first steps towards making a website accessible, optimised for search engines and compliant.
How is it measured?
The use of alternative text is measured for every element of every webpage that could use it (typically images, audio and video).
The score is taken from the proportion of alternative text that is specified for each of those elements, weighted for the relative importance of the pages they appear on. The best possible score would come from using alternative text everywhere that could use it.
Images with a width or height of one pixel are excluded automatically – i.e. they do not need alternative text to be specified. Almost exclusively these images are used for tracking purposes, e.g. Analytics ‘beacon’ image, or as layout hacks, and they have no impact on accessibility or SEO.
Links that contain only an image – but have no alternative text – are penalised far more than standalone images. This images are essentially blank links – neither search engines nor visually impaired users can tell what they point to.
Where identified, particularly bad or useless Alternative text is also penalised. For example, alternative text such as “Image01.jpg” does not describe an image to a blind person or search engine.