Alt text for SEO: the complete guide for e-commerce stores
· alt text · SEO · WCAG · e-commerce
A Shopify store with 400 products and no alt text is invisible to Google Images. That is tens of thousands of potential image search impressions going nowhere — and it is far more common than most store owners realise. Alt text for SEO is one of those tasks that looks trivial until you work out how much organic traffic it affects.
This guide covers what actually matters: how Google reads alt attributes, what good product alt text looks like versus bad, the most common mistakes, and where WCAG 2.1 AA requirements and search optimisation overlap.
How Google reads image alt text
Google cannot see images the way a human can. It reads the alt attribute on an <img> tag to understand what the image shows. That text feeds into three ranking signals at once.
First, it helps the image appear in Google Images search. Second, it adds relevance context to the surrounding page — a product page with twenty images, each with descriptive alt text, sends a stronger topical signal than the same page with empty attributes. Third, it affects how Google indexes the page for assistive technology crawls, which have become more relevant as accessibility becomes a ranking factor under Core Web Vitals and the evolving quality guidelines.
Worth noting: Google's John Mueller confirmed in 2023 that alt text is "one of the main ways we understand what an image shows." It is not a vanity metric.
The mechanic is simple. When Googlebot crawls your page, it reads the alt attribute as a text signal. If that attribute is empty or missing, the image contributes nothing to the page's topical authority. If it is keyword-stuffed, Google's spam filters treat it the same as hidden text.
What good alt text actually looks like for product images
Here is the practical difference between alt text that helps SEO and alt text that does not.
| Image | Bad alt text | Good alt text |
|---|---|---|
| Navy blue linen shirt, men's | img_3847.jpg | Men's navy blue linen shirt, short sleeve |
| Leather ankle boots | shoes | Women's tan leather ankle boots with side zip |
| White ceramic coffee mug | mug | White ceramic coffee mug, 350ml, dishwasher safe |
| Decorative banner image | banner | (empty — alt="") |
A few things to notice in that table. Descriptive alt text names the product, colour, material, and relevant attribute in under 125 characters. It does not start with "image of" or "photo of" — Google already knows it is an image. It does not repeat the filename. And for decorative images like hero banners or dividers, the correct alt text is literally nothing — an empty alt="" attribute tells screen readers and search engines to skip it.
In HTML, the difference looks like this:
<!-- Bad: missing alt, contributes nothing to SEO -->
<img src="navy-linen-shirt.jpg">
<!-- Bad: keyword stuffed, triggers spam filters -->
<img src="navy-linen-shirt.jpg" alt="buy linen shirt linen shirts cheap linen shirt men">
<!-- Good: descriptive, specific, readable -->
<img src="navy-linen-shirt.jpg" alt="Men's navy blue linen shirt, short sleeve">
<!-- Good: decorative image correctly marked -->
<img src="sale-banner.jpg" alt="">
The 125-character limit is a practical guideline, not a hard rule — screen readers typically truncate longer descriptions, and overly long alt text tends to dilute the keyword signal rather than strengthen it.
Common alt text SEO mistakes in e-commerce
Most store owners make the same five errors. Three of them happen automatically because of how e-commerce platforms handle images by default.
Filenames as alt text. Shopify, WooCommerce, and PrestaShop all fall back to the image filename when no alt attribute is set. DSC_0047.jpg tells Google nothing. Neither does product-image-1. If you have never explicitly set alt text on your product images, check — you probably have hundreds of these.
One alt text for multiple sizes. Product photos often exist in three or four variants: main image, zoom, lifestyle shot, packaging. Each one is a separate image. Each one needs its own relevant alt text. A zoom image of stitching detail on a jacket warrants Merino wool stitching detail on the shoulder seam — not the same generic text as the main product shot.
Alt text that matches the page title exactly. If your page title is "Men's Navy Linen Shirt — Summer Collection" and every image on the page has that exact same alt text, Google sees repetition, not depth. Vary the descriptions. Cover colour, material, use case, size in different images.
Skipping alt text on non-product images. Navigation icons, trust badges, rating stars — these are functional images. They need alt text too. "Trustpilot 4.8 stars" or "Free delivery icon" are both correct and useful.
Empty alt on images that are not decorative. A product image with alt="" is a WCAG failure and an SEO miss. The empty attribute is correct only for images that carry no information — backgrounds, dividers, decorative flourishes.
Where alt text SEO and WCAG 2.1 AA requirements meet
This is where a lot of guides skip over something practical. WCAG 2.1 Success Criterion 1.1.1 requires that every non-decorative image has a text alternative. That is the same requirement that makes alt text useful for Google. The goals are aligned, not in conflict.
The practical implication for store owners: if you write alt text that passes a WCAG accessibility check, it will also be good for SEO. The two standards share the same core requirement — describe what the image shows, be specific, and do not stuff keywords or leave it empty.
There is one real difference. SEO alt text benefits from including relevant product keywords naturally. WCAG does not penalise this, as long as the description is genuinely useful to a screen reader user who cannot see the image. The test: if you read the alt text to someone who cannot see the page, would they understand what the image shows? If yes, it works for both.
For the European Accessibility Act (EAA), which has applied since June 2025, this matters beyond rankings. If your store sells to EU consumers, missing alt text is both an accessibility compliance gap and an SEO problem — fixing it once addresses both.
How to audit your existing alt text
Running a manual audit on 400 product images is not realistic. There are four approaches, roughly in order of effort.
Browser DevTools works for spot-checking individual pages. Right-click any image, inspect the element, and look at the alt attribute value. Fast for a single page, not scalable.
Google Search Console's Coverage report shows indexed images but does not surface missing alt text directly. It is useful for confirming that Google Images is indexing your product images at all.
A dedicated WCAG scanner tests accessibility requirements — including missing alt text — across multiple pages at once. The results double as an SEO audit. Altvisor's free WCAG site scan covers alt text, form labels, document language, and semantic structure in one pass.
Bulk generation tools are the only practical option for large catalogues. A store with 1,000 products accumulates alt text debt through normal trading — new images added by suppliers, seasonal refreshes, variant photos. Manual fixes do not scale; automation does.
Run a free WCAG scan on your storefront to see exactly where you stand — then start free to fix image alt text at scale.