The Definitive Guide to ALT Text
ALT text is one of the oldest, simplest, and most overlooked features of the web. It's also one of the most important. Here's everything worth knowing — what it is, why it matters, how to write it well, and how it got here.
What is ALT text?
ALT text (short for "alternative text") is a written description of an image. On a web page it lives in the image'salt attribute; on social platforms it's the "description" or "alt" field you fill in when you attach a photo.
It does three jobs at once:
- It's read aloud by screen readers, so people who can't see the image still know what it shows.
- It appears when an image fails to load — a broken link, a slow connection, a data-saver setting.
- It's read by search engines, which use it to understand and index images.
The test for good ALT text is simple: if you couldn't see this image, what would you need to be told so you didn't miss anything?
Why ALT text matters
The World Health Organization estimates that at least 2.2 billion people live with some form of vision impairment. Millions of them navigate the web with screen readers — software that reads a page aloud, top to bottom. When that software reaches an image with no ALT text, it says something like "image", or reads out a meaningless file name like "IMG_4021.jpg". The content of the picture simply vanishes.
Beyond access for its own sake, ALT text matters because:
- It's frequently required by law. The Americans with Disabilities Act (ADA), Section 508 of the Rehabilitation Act, the international WCAG standard, and the EU's European Accessibility Act all treat text alternatives as a baseline requirement — not a nice-to-have.
- It improves search visibility. Descriptive ALT text is one of the clearest signals search engines have about what an image contains.
- It's resilient. On a train, on bad Wi-Fi, on a data plan running low — when the image doesn't arrive, the words still do.
- It helps everyone. This is the "curb-cut effect": a ramp built for wheelchairs also helps strollers, luggage, and delivery carts. Accessibility features quietly make things better for all of us.
The accessibility standard, in one line: WCAG Success Criterion 1.1.1 ("Non-text Content") — the very first checkpoint in the guidelines — says all non-text content needs a text alternative. It's a Level A requirement, the most fundamental tier.
How to write good ALT text
Good ALT text is accurate, concise, and written for context. It describes not just what an image is, but what it's doing on the page. A photo of a lighthouse in a travel article and the same photo used as a "download our app" button need completely different descriptions.
Do
- Describe what matters for the context.
- Keep it concise — usually a sentence or two.
- Include any text that appears in the image.
- For buttons and links, describe the action or destination.
- Use empty
alt=""for purely decorative images so screen readers skip them.
Don't
- Start with "image of" or "photo of" — the screen reader already says it's an image.
- Stuff in keywords for SEO. It's dishonest and it hurts real users.
- Leave it blank on meaningful images, or dump the file name.
- Over-describe every pixel — convey the point, not an inventory.
- Repeat a caption that's already right next to the image.
For complex images — charts, diagrams, infographics — pair a short ALT text with a longer description nearby in the page text, so the detail is available to everyone.
Where ALT text came from
ALT text is nearly as old as the web image itself. It has been part of the HTML standard since the very beginning — the story is really about the world slowly catching up to using it.
- 1993The
<img>tag is proposed for NCSA Mosaic, bringing inline images to the web. It ships with no built-in text alternative. - 1995HTML 2.0 (RFC 1866) formalizes the
altattribute, making a text alternative an official part of the language. It has been in every HTML version since. - 1998The U.S. amends Section 508 of the Rehabilitation Act, requiring federal technology — including websites — to be accessible.
- 1999The W3C publishes WCAG 1.0, the first Web Content Accessibility Guidelines. Text alternatives are checkpoint one.
- 2008WCAG 2.0 arrives and becomes the global reference standard, with "Non-text Content" (1.1.1) as its foundational Level A criterion.
- 2016–2018Social platforms catch on: Twitter adds ALT text in 2016; Instagram follows in 2018 with both automatic and manual descriptions.
- 2018WCAG 2.1 extends the guidelines for mobile, low vision, and cognitive accessibility.
- 2023–2025WCAG 2.2 is published (2023). The European Accessibility Act takes effect (June 2025), pushing accessibility requirements across private-sector digital products in the EU.
The future of ALT text
For thirty years, the biggest problem with ALT text hasn't been the technology — it's been the effort. Writing a thoughtful description for every image, everywhere, is real work, and so most images on the web still have none. Three shifts are changing that:
- AI that writes the first draft. Modern vision models can look at an image and produce a solid, accurate description in seconds. That's exactly what ALTtext does — it turns "I don't have time" into "here's a starting point, edit if you like."
- Descriptions that travel with the file. The IPTC photo-metadata standard now includes accessibility fields, so an image's ALT text can be embedded in the file itself and carried across every platform it's posted to.
- Culture and law, together. Communities like Mastodon and Bluesky have made ALT text a norm rather than an afterthought, while laws like the European Accessibility Act make it a requirement. Expectation and obligation are finally pointing the same way.
The destination is simple: ALT text on every image, by default. Not because a checklist demands it, but because leaving people out was never acceptable — and now there's no good excuse left.
Where ALTtext fits
ALTtext exists to remove the last excuse. Drop in any image and it writes accessible ALT text in seconds — free, with no account and nothing to install. Edit it, copy it, and paste it wherever you need it. It began as a feature inside a social-media app and grew into something that deserved to stand on its own and belong to everyone.
The basics are free for everyone, forever. If you need it at volume — or for a team, or via API — ALTtext Pro lifts the limits and keeps the free tier running for the next person.