When optimizing a webpage, most people focus heavily on their written content, headings, and meta tags. But what about the visual elements?
Search engines have incredibly advanced algorithms, but they still cannot “see” images the way human beings do. To understand what a picture is about, Google relies on a tiny snippet of HTML code: the Alt Text (Alternative Text).
However, writing alt text isn’t as simple as stuffing your target keywords into every single <img> tag on your site. In fact, doing that can actually harm your SEO and ruin your site’s accessibility.
In this complete guide, we will cover the SEO best practices for writing perfect alt text, and the critical exception where you should intentionally leave it completely empty.
Why Alt Text is Crucial for SEO and Accessibility
Alt text serves three primary purposes on the web:
- Web Accessibility (Crucial): Screen readers used by visually impaired visitors will read the alt text aloud, allowing them to understand the visual context of the page.
- Failsafe Display: If an image fails to load due to a slow connection or a broken link, the browser will display the alt text in its place.
- SEO Ranking Signal: Google uses alt text, along with the text surrounding the image, to understand the subject matter. This is the primary way your images rank in Google Image Search, which can drive massive amounts of organic traffic to your site.
Best Practices: How to Write Perfect Alt Text
Writing good alt text is about being descriptive, concise, and natural. Imagine you are describing the image to someone over the phone.
1. Be Specific and Descriptive
Do not use generic terms.
- ❌ Bad:
<img src="shoes.jpg" alt="shoes"> - ✅ Good:
<img src="shoes.jpg" alt="Red Nike running shoes on a wooden table">
2. Do Not Keyword Stuff
Google’s spam algorithms easily detect keyword stuffing in alt attributes.
- ❌ Spammy:
<img src="shoes.jpg" alt="buy cheap shoes online red sneakers best running shoes"> - ✅ Good:
<img src="shoes.jpg" alt="Side profile of red Nike running shoes">
3. Keep it Under 125 Characters
Most screen readers stop reading alt text after 125 characters. Keep your descriptions punchy and to the point.
4. Don’t Include “Image of” or “Picture of”
Screen readers automatically announce that the element is an image, so writing alt="Picture of a dog" is redundant. Just write alt="A golden retriever playing in the grass".
The Big Exception: When to Leave Alt Text Empty
Here is a technical SEO secret that many beginners miss: Not every image needs alt text.
If an image is purely decorative and adds no contextual value to the content, you should leave the alt attribute empty. This is known as a “null” alt attribute:
<img src="divider.png" alt="">
When to use an empty alt attribute:
- Background patterns or brand graphics used purely for visual aesthetics.
- Horizontal divider lines or stylistic bullet points.
- Social media icons or symbols that are immediately followed by text explaining what they are (e.g., a magnifying glass icon next to the word “Search”).
Why? If you add descriptive alt text to a decorative graphic (like alt="blue squiggly line"), a screen reader will read it out loud, creating a frustrating and confusing experience for visually impaired users.
Important Note: You must still include the alt="" attribute itself. If you completely omit the alt attribute from the HTML, some screen readers will default to reading the raw file name (e.g., “divider_v2_final.png”), which is terrible for user experience.
How to Audit Your Missing Alt Attributes Instantly
Checking your website’s source code to ensure every single image has the correct alt attribute is a massive headache, especially on image-heavy WordPress sites.
You can automate this process in seconds using FunSEO.
Our free, instant technical SEO scanner will crawl your URL and specifically audit your images. The FunSEO engine will calculate the exact percentage of your images that have alt attributes. It will also flag any images with empty alt attributes (alt=""), allowing you to quickly verify if those images are genuinely decorative or if they are missing crucial descriptive text.
No login required. No credit card. Just drop your URL into FunSEO today and ensure your images are fully optimized for both Google and your users.