The Importance of Alt Tags: Small Image Detail, Big SEO Impact

When you upload an image to your website, there's a small box most people leave empty. It takes thirty seconds to fill in, costs nothing, and quietly works for you in three different ways at once. That box is the alt tag — and on any site that relies on Google for traffic, leaving it blank is one of the easiest wins you're giving away.

What an alt tag actually is

An alt tag (technically the alt attribute of an image) is a short written description of what a picture shows. Visitors normally never see it — but screen readers read it aloud to blind and visually impaired users, and Google reads it to work out what your image — and your page — is about.

A good one describes the image plainly: "man fitting a replacement boiler in a kitchen", not "IMG_4021" or worse, a keyword-stuffed sentence. If the image is purely decorative, an empty alt tag is actually correct — you're telling screen readers to skip it.

Why it matters for SEO

Google can't see images. Its systems read the file name, the surrounding text and the alt tag to decide what a picture shows, and whether it should appear in Google Images. Every image you've optimised is another door into your site: for e-commerce and product-led businesses, Google Images is a meaningful slice of traffic that costs you nothing extra to earn.

Alt tags also reinforce what the page is about overall. A page about boilers with images correctly described as boilers, radiators and pipework tells Google the page is genuinely on-topic. That consistency builds relevance — and relevance is what rankings are made of.

Accessibility isn't optional

Screen readers announce images using their alt text. When it's missing, users hear the file name or nothing at all — a broken experience for anyone who can't see the screen. Beyond doing the right thing, there's a legal angle: the Equality Act expects UK websites to be accessible, and accessibility lawsuits are increasingly common. Well-written alt text is one of the single biggest accessibility improvements a site can make.

How to write a good alt tag

• Describe the image in plain English — as if describing it over the phone.
• Keep it short — aim for under 125 characters; screen readers truncate long ones.
• Include your keyword naturally where it genuinely fits — never force it.
• Skip "image of..." — screen readers already announce it's an image.
• Leave decorative images empty (alt="") so they're skipped.

What to do next

Open your media library and work through your most important pages first — home page, key product or service pages, recent blog posts. Describe every meaningful image in a few honest words. On WordPress you can edit alt text one image at a time in the media library, or as you insert images into posts.

It's thirty seconds per image for a permanent improvement to your SEO, your accessibility and your Google Images visibility. Very few fixes offer that kind of return — we help businesses make these improvements every week, and this is usually where we start.