What Is Alt Text And How Do You Write It Properly

Alt text is one of those things that sits quietly in the background of every well-built website, rarely celebrated and yet absolutely essential to getting things right online. Whether you are managing a large e-commerce platform, running a blog, or overseeing a corporate website, understanding what alt text is and how to write it properly can have a meaningful impact on your search engine performance, your site's accessibility standards, and ultimately the experience you deliver to every person who visits your pages. It is not a complicated concept, but it is one that is consistently misunderstood, overlooked, or handled badly, and that matters more than many people realise.

What Is Alt Text?

Alt text, short for alternative text, is a written description that is applied to an image within the HTML of a web page. It sits inside the image tag and is not visible on the page itself under normal circumstances. However, it serves several very important functions that go far beyond just being a line of code that nobody reads.

When a screen reader is used by someone who is visually impaired, the alt text is what gets read aloud to describe what the image shows. When an image fails to load due to a connection issue or a broken file path, the alt text is what appears in its place. And when search engine crawlers like Google's image indexing system encounter an image on your page, they rely heavily on the alt text to understand what that image depicts and how relevant it is to the surrounding content.

In short, alt text is the bridge between your visual content and both the people and systems that cannot see it directly.

Why Alt Text Matters for SEO

From a search engine optimisation perspective, alt text gives you an additional opportunity to contextualise your content and signal relevance to search engines. Google has become increasingly sophisticated in its ability to interpret images using machine learning and computer vision, but it still uses alt text as an important input when deciding how to rank and index your images, and how to associate them with the surrounding page content.

If you are targeting specific keywords or trying to rank for particular searches, well-written alt text that naturally incorporates those terms can support your broader SEO strategy. Image search is also a channel that many website owners neglect entirely, but with proper alt text in place, your images have a genuine opportunity to appear in Google Image search results and drive additional traffic to your site.

Beyond rankings, alt text also contributes to your site's overall quality signals. A website that has clearly been put together with care, where every image has a meaningful description, tells search engines something positive about how seriously you take the user experience.

Accessibility Is Not Optional

It is worth being direct about this. Writing proper alt text is not just a best practice for SEO, it is a matter of accessibility and, in many cases, a legal requirement. Organisations such as the Web Accessibility Initiative (WAI) under the World Wide Web Consortium have established clear guidelines through the Web Content Accessibility Guidelines (WCAG) that set out how images should be described for users who rely on assistive technologies.

For a person using a screen reader, an image without alt text is essentially invisible in any meaningful sense. They know something is there, but they have no idea what it shows or why it is on the page. For decorative images that carry no informational value, an empty alt attribute is actually the correct approach, because it tells the screen reader to skip over the element. But for any image that contributes to the meaning or message of your content, descriptive alt text is absolutely necessary.

How to Write Alt Text Properly

Writing effective alt text is a skill, and like most skills, it improves significantly once you understand the principles behind it. The core question you should always ask yourself is: if someone cannot see this image, what do they need to know about it to understand what this page is communicating?

Be descriptive but concise

Alt text should describe the image clearly without becoming a paragraph-long essay. In most cases, a single sentence of around ten to fifteen words is sufficient. If you are writing alt text for a photograph of a person giving a presentation in front of a whiteboard in an office setting, you would write something that captures that scene rather than simply writing "photo" or leaving the field blank entirely. Describe what is actually happening in the image, who or what is in it, and any relevant context that adds meaning.

Incorporate your keyword naturally

If the image is genuinely relevant to a keyword you are targeting, it makes sense to include that term in the alt text. However, this should feel natural rather than forced. Keyword stuffing in alt text is something Google recognises and does not reward. Write the description as if you were explaining the image to a colleague over the phone, and if the keyword fits naturally into that explanation, include it. If you have to contort the sentence to squeeze it in, leave it out.

Avoid starting with redundant phrases

There is no need to begin your alt text with phrases like "image of" or "picture showing" because screen readers already announce that an image is being encountered. Starting your description directly with the content of the image is the cleaner and more effective approach. For example, rather than writing "image of a red running shoe on a white background," you would simply write "red running shoe on a white background."

Treat decorative images differently

Not every image on a page needs a descriptive alt text. Icons used purely for visual styling, abstract background patterns, and purely decorative dividers are examples where an empty alt attribute, written as alt="", is the correct choice. This signals to screen readers and search engines alike that the image carries no informational value and can be safely ignored.

Common Alt Text Mistakes to Avoid

Even experienced web professionals make mistakes with alt text, and understanding where things tend to go wrong is useful if you want to get it consistently right across your entire site.

Leaving the alt attribute blank on informational images is perhaps the most common error. It is often a result of rushing through the content upload process rather than a deliberate decision, but the impact is the same regardless of intent. Another frequent mistake is using the file name of the image as the alt text. A file name like "IMG_4872.jpg" or "banner-graphic-v3-final.png" tells nobody anything useful and does nothing for your SEO or your users.

Writing identical alt text for multiple different images is also problematic. Each image should have its own unique description that reflects what it actually shows, not a generic phrase applied across an entire image library as a shortcut.

Making Alt Text Part of Your Standard Process

The most effective way to ensure your alt text is handled properly is to build it into your standard content creation and publishing workflow rather than treating it as an afterthought. Whether you are using WordPress, Shopify, or any other content management system, there will be a dedicated alt text field available when you upload or insert an image. Make completing that field a non-negotiable step in your process, and if you manage a team of content creators, make sure they understand why it matters and how to do it well.

If you have a large existing library of images that currently lack alt text, it is worth undertaking an audit. Tools like SEMrush and Ahrefs can flag missing alt text across your site as part of a broader technical SEO audit, giving you a clear picture of where the gaps are.

Getting It Right From Here

Alt text is one of those foundational elements of good web practice that rewards the effort you put into it across multiple dimensions at once. Done well, it supports your SEO, improves your accessibility, and demonstrates a level of care for your users that search engines notice and appreciate over time. It does not require specialist knowledge or expensive tools to get right. It requires clarity of thought, a consistent process, and the discipline to treat every image on your website as something that deserves a proper, considered description. Start auditing your current content, build better habits going forward, and you will be placing your site in a stronger position on every front that matters.