What make good Alt Text description?

Good alt text is written with both visitors and search engines in mind. A few practical principles:

Be specific and succinct. Describe what's actually in the image without unnecessary embellishment. A useful trick: imagine briefly describing the image to someone over the phone. Aim for no more than 125 characters, as most screen readers stop reading after that point.

Don't start with "Image of…" or "Picture of…" It's already clear to a screen reader or search engine that this is an image description. If it's useful to give context on the type of image — for example a headshot, illustration, chart, or screengrab — that's worth including instead.

Use keywords sparingly. If a relevant keyword fits naturally into a true, accurate description, that's a helpful bonus for SEO. But never force it in, and avoid keyword stuffing — alt text should always describe the image honestly first.

Avoid repeating information that's already on the page. If an adjacent caption or heading already says what the image shows, the alt text doesn't need to repeat it.