What Is an Alt Tag: Why It Matters & How to Write One

Imagine you run an online store selling handcrafted jewellery. You’ve got beautiful product images, but when potential customers search for “gold-plated earrings,” your site doesn’t show up in Google Image Search. Worse, people using screen readers, who may be unable to actually see those images, are left with very little information that lets them visualise it in their head. This isn’t just an inconvenience—it’s a huge missed opportunity for visibility, engagement, and revenue – not to mention SEO too…

That’s where alt tags come in. Also known as image alt text, alternative tags, or img alt attributes, they describe images to search engines and users who can’t see them. More than just an accessibility feature, as we’ve mentioned, an alt text plays a crucial role in SEO, user experience, and AI-driven search (think Google’s Search Generative Experience (SGE) and visual search).

So, why should businesses care about alt tags? The answer is simple: they improve website accessibility (which is good for your SEO), help images rank in search results, and enhance user experience, making your content more engaging and inclusive. By the end of this guide, you’ll know exactly how to write alt tags that boost rankings, drive traffic, and improve your site’s accessibility.

What Is an Alt Tag?

Many people confuse the terms ‘alt text’, ‘alt tags’, and ‘alternative tags’, but they all serve the same purpose—to describe an image when it can’t be seen. The difference? Alt text is the description itself, while alt tags refer to the HTML attribute where this text is placed.

Here’s how an img alt attribute looks in source code:

<img src=”https://seeksocial.co.uk/wp-content/uploads/2024/12/what-are-market-niches.jpg” alt=”what are market niches”>

Search engines use alt text to understand what an image represents, helping them categorise and rank it in Google Image Search. This is especially important as Google’s AI (MUM & BERT algorithms) increasingly rely on context to understand multimedia content.

In short, alt tags are not just about accessibility—they help Google understand your content better too, improving your website’s SEO performance.

Why Are Alt Tags Important?

Making the Web Inclusive

Accessibility should be a top priority for every website. Screen readers—used by people with visual impairments—rely on alt text to describe images aloud. If an alt tag is missing, a screen reader might just say “image,” providing no useful information to the user about that image.

In 2021, missing alt text accounted for 61% of all homepage accessibility errors, highlighting how many websites still fail to implement this simple yet vital feature. Legal compliance is also a factor, as the W3C Web Content Accessibility Guidelines (WCAG) and regulations like the UK Equality Act 2010 require websites to be accessible to all users.

SEO Benefits: Image Search & Beyond

Alt tags are a critical factor for ranking in Google Images. A case study by HubSpot revealed that optimising image alt text increased image search traffic by 779% in under a year, proving that search engines prioritise images with descriptive alt text.

Google’s Search Generative Experience (SGE) and Visual Search are making this even more important. AI-driven search engines can now recognise image content, but alt tags still provide crucial context. Without them, your images are unlikely to rank well in search.

A Better User Experience

Not all users will see your images. An article from Forbes states that 73% of users report that they’ve experienced a mobile website that was too slow to load, meaning images often fail to appear. With proper alt text, users can still understand the content even when images don’t load—keeping them engaged instead of bouncing off your page.

How to Write Alt Tags: The Perfect Formula

Writing effective alt text isn’t just about description—it’s about context, specificity, and SEO optimisation. Let’s look at examples of good vs. bad alt tags:

Good Alt Text: “Golden retriever puppy playing with a tennis ball in a park”

Bad Alt Text: “Dog playing”

Why It Matters: Specificity improves SEO and user understanding

Good Alt Text: “Stack of organic blueberry pancakes with honey drizzle on a wooden table”

Bad Alt Text: “Pancakes breakfast”

Why It Matters: Better keyword relevance for food-related searches

How long should alt text be?

There’s no strict limit, but Google recommends keeping alt text concise yet descriptive. A good rule of thumb is to keep them under 125 characters, ensuring screen readers can process the information easily.

Common Alt Tag Mistakes & How to Avoid Them

Despite their importance, many websites get alt tags wrong. Here’s what to avoid:

1. Overstuffing keywords: “Best SEO alt text image alternative keyword boost”—this feels unnatural, disrupts user experience, and may negatively impact your SEO ranking, as Google discourages keyword stuffing in alt text.
2. Leaving alt text blank: “alt=””—if an image conveys important information, leaving it empty is a mistake.
3. Using redundant phrases: “Image of…” or “Picture of…”—screen readers already recognise it’s an image, so skip these unnecessary words.

With AI-powered image recognition improving, Google no longer relies solely on alt text, but well-written descriptions still give you an SEO advantage.

Advanced Alt Tag Strategies: Optimising for AI & Future Search

AI-Powered Image Search: What’s Changing?

Google’s MUM algorithm understands images using computer vision, but alt text still plays a key role. If Google misinterprets your image, the Cloud Vision API can show how AI sees it—allowing you to adjust your alt tags accordingly.

Alt Tags for Local SEO

Alt text isn’t just about rankings—it can boost local SEO. For example, rather than “Cake shop”, an optimised alt tag for a bakery might read:

“Best vegan bakery in London – chocolate cake display with fresh raspberries”

This increases the chances of appearing in local image searches, driving nearby customers to your store.

E-Commerce & Conversions

For e-commerce businesses, alt tags directly impact sales. Amazon, for example, uses keyword-rich alt text to optimise product listings. If you run an online shop, your product images should have detailed, search-friendly alt text that helps customers find your items.

Tools & Resources to Help You Write Alt Tags Efficiently

Manually writing alt text can be time-consuming, but AI-powered tools can help:

A downloadable Alt Text Audit Template can help businesses check and optimise existing alt tags for better performance.

Conclusion: It’s Time to Optimise Your Alt Tags

If you’ve made it this far, you know why alt tags are essential. They improve accessibility, boost SEO, and enhance user experience.

So, what’s next? Audit your website and optimise your image alt text today! Not sure where to start? Sign up for a free SEO audit, and we’ll help you ensure your alt tags are fully optimised.

Your website deserves better rankings—start optimising your alt text now.