Alt text vs media descriptions: What’s the difference, and when to use them?

This year I took a course on Inclusive Communication (Bold Type by Ettie Bailey-King) and was surprised by how much time we spent on alt text - not just what it is, but actually writing it, submitting it for feedback and editing, over and over. It’s a whole thing.

I get asked about alt text a LOT, so I’m passing some of that knowledge on!

Alt text and media descriptions are two of the simplest ways to make your content more inclusive. They sound similar, but they’re not the same and they serve different purposes (and both will help your SEO!)

What is Alt Text?

Alt text is ‘hidden’ metadata that describes the essential content of an image. Screen readers read it aloud, and it appears on screen if an image doesn’t load.

Use alt text on all images, but pay particular attention when:

The image conveys information someone could otherwise miss (e.g. charts, quotes, diagrams)
The image is abstract or nuanced and was chosen for a reason (e.g. a yellow balloon to represent a feeling of optimism)

How long should it be?

Some screen readers may cut off alt text at around 100–120 characters. That’s one sentence, maybe two. (For my old school Twitter crew, that’s less than a Tweet!) If it needs more detail, that’s when you might want to use an image description as well.

Alt text example :

‘Two people sitting at a desk reviewing a brand moodboard with a laptop and colour swatches.’

Definitely not going to win any creative writing awards, but it's not supposed to - function over form!

Make it stand out

Whatever it is, the way you tell your story online can make all the difference.

What is a media description?

A media description (usually an image description and often shortened to ‘ID’) is visible text added directly into your content (not behind the scenes like alt text). It’s a sentence or short paragraph and it can benefit everyone, not just people using assistive tech.

Image descriptions are especially useful for:

People with low vision who may not be able to interpret visual detail
People who prefer written context over interpreting images
Anyone browsing without visuals (maybe because of image blockers or low bandwidth)
Social media, website platforms and content schedulers where alt text isn’t supported (this is usually the case with audio, video, pdfs and GIFs)

Media description example:

‘ID: Lauren leans over a desk scattered with colour swatches and half-formed logo sketches, deep in the flow of designing a new brand concept in a cosy studio with sunlight streaming in.’

Best practices to start using now:

Use alt text to describe the meaning (what and why), not every pixel
For logos, write the business name instead of describing the logo
There’s no need to include ‘image of’ - screen readers already announce that
Use alt=" " for decorative images
Include any text shown in the image
Pair alt text with longer descriptions for complex visuals
Keep the tone neutral and factual
Don’t keyword-stuff for SEO
If you work in a team, create an internal guide for consistency
Remember to check if there's already alt text and/or media descriptions when you repost images - chances are you'll need to add them again
GIFs, video and pdfs need descriptions too!
By the way pdf documents themselves need alt text, but I'll write about that another day…

Can AI write alt text?

AI can generate quick first drafts, and it’s handy when you’re working at scale, but of course it comes with limits.

The main issue is that it doesn’t understand intent or nuance. It can tell you what’s there, not why it matters.

That's all, folks!

If you've found this post helpful please do let me know. It helps me shape my content!

Ciao for now,

Lauren

Alt text or media description?