Image Alt Tag
Checker Free

What Is an Image Alt Tag and Why Does It Matter for SEO?

An image alt tag is an HTML attribute you add to every img element. It looks like this: alt="description of the image". The alt attribute serves two jobs at the same time. First, it tells Google what the image shows, since Google cannot see images the way a human does. Second, it is read aloud by screen readers for visually impaired users, making your website accessible to millions of people.

What Happens When Alt Text Is Missing?

When an image has no alt attribute, Google skips it completely. That image will never appear in Google Image Search, Google Discover image carousels, or visual search results. You lose all the SEO value that image could have brought to your page. For users relying on screen readers, the reader will either say "image" with no context, or read out the file name, something like "IMG_4321.jpg", which tells the user nothing useful. Our Free image alt tag checker finds every missing alt attribute on your page in seconds.

Is Empty Alt Text the Same as Missing Alt Text?

No, and this difference is important. Missing alt (no alt attribute at all) is always an error for any image that carries meaning. Empty alt (alt="" with nothing inside) is actually correct for purely decorative images like background shapes, dividers, or purely decorative icons. Empty alt tells screen readers to skip the image entirely, which is the right behaviour for decoration. Our tool detects both cases and treats them differently based on context.

How to Write Good Alt Text That Ranks in Google Image Search

Good alt text is a short, accurate sentence that describes exactly what the image shows. It is not a list of keywords. It is not "image of a dog." It is not a file name. It is not a paragraph. Think of it as what you would say to someone on a phone call to describe the image in one sentence.

The Right Length for Alt Text

Keep alt text between 8 and 125 characters. Screen readers stop reading alt text after 125 characters, so anything beyond that is wasted. Very short alt text like "dog" gives Google almost no useful information. A good target is one clear sentence of around 10 to 15 words. For example: "Golden retriever puppy playing on green grass in a garden" is much better than "dog" or "cute-puppy-photo.jpg".

Should You Include a Keyword in Alt Text?

Yes, if the image is genuinely relevant to your target keyword, include it once, naturally. If your page is about free SEO tools and you have a screenshot of a dashboard, writing "free SEO tools dashboard showing keyword rankings" is correct. Do not force a keyword into alt text for images that have nothing to do with that keyword. Google understands context and will see forced keywords as a spam signal. Use our Free keyword coverage checker to see how many of your images already mention your target keyword.

What to Avoid in Alt Text

Do not start with "image of" or "photo of" because Google already knows it is an image. Do not use ALL CAPS as this affects how screen readers pronounce the text. Do not repeat the same keyword three or more times. This is keyword stuffing and can trigger a Google penalty. Do not leave the file name as the alt text. File names like "DSC00123.jpg" are meaningless to both Google and users. Our alt tag checker flags every one of these mistakes automatically.

Image Attributes That Affect Core Web Vitals and Page Speed

Alt text is not the only thing that matters on an img tag. Google also looks at several other attributes when scoring your page for Core Web Vitals, which is the set of speed and user experience metrics that directly affect rankings. Our Free image audit checks all of these in one pass.

Width and Height Attributes Prevent Layout Shift

When an image loads slowly on mobile, and you have not told the browser how big the image will be, the page jumps and shifts as the image appears. This is called Cumulative Layout Shift (CLS) and it is one of Google's Core Web Vitals signals. The fix is simple: always add both width and height attributes to every img tag. This lets the browser reserve the right amount of space before the image loads, so nothing shifts. Missing these attributes is one of the most common causes of a bad CLS score.

lazy Loading Speeds Up Pages Without Losing Rankings

Adding loading="lazy" to images that are not visible in the first screen tells the browser to wait before downloading them. This makes the page load much faster for the user. Google actively rewards pages that implement lazy loading because it improves Largest Contentful Paint (LCP), which is the time until the main content is visible. Only the first one or two hero images should not use lazy loading since those need to load immediately.

WebP and AVIF Formats Make Images Smaller

Images in JPG and PNG format are much larger in file size than the same image in WebP or AVIF format. WebP is typically 25 to 35 percent smaller than JPG at the same visual quality. AVIF is even smaller. Smaller images mean faster pages, lower bandwidth costs, and better Core Web Vitals scores. Our tool detects legacy format images on your page and flags them so you know which ones to convert first.