Free Image Alt Tag Checker

Missing alt text, empty alt, and what an alt tag checker can't see.

Alt text is the one sentence a page gives for each picture, read aloud to people who cannot see it and read as text by every crawler. Here is what it is for, the difference most checkers blur, and how to write it for a firm whose images carry claims.

What alt text is, and why people call it an alt tag

Image alt text is the text alternative for an image, written in the alt attribute of the <img> element. It is an attribute, not a tag, but "alt tag" is the name most people search for, so both appear on this page and mean the same thing. It lives in the HTML beside the image's address:

<!-- informative: the text does the image's job -->
<img src="k1-part-3.png" alt="Schedule K-1, Part III, box 1 highlighted">

<!-- decorative: empty, so assistive technology skips it -->
<img src="leaf-divider.svg" alt="">

<!-- missing: no alt attribute at all -->
<img src="IMG_4471.jpg">

Three states, and they are not two versions of the same thing. The first tells a reader what the image shows. The second tells assistive technology the image is decoration and should be passed over. The third says nothing, and leaves every reader of the HTML to guess.

Who reads it

Screen readers. A person using a screen reader hears the alt text in place of the image. When the attribute is missing there is nothing to read, and the W3C's own failure technique for this case, F65, notes that some assistive technology compensates by reading out the file name instead. IMG_4471.jpg, spoken aloud, is the sound of a missing alt attribute.

Image search. Google's image SEO guidance calls alt text the most important attribute for giving an image metadata, and says Google uses it along with computer vision and the page's content to understand what an image is about.

Anyone whose images don't load. On a slow connection or a blocked image host, the browser shows the alt text where the picture should be.

Every crawler that reads HTML. Search crawlers and the crawlers behind AI assistants receive the page as text. The alt attribute is text; the picture is not. Whatever a chart says, a machine reading the HTML gets only what the alt text and the surrounding copy say about it.

Missing alt versus alt="": the difference most checkers blur

Not every image needs describing. A divider, a background flourish, an icon sitting beside a text label that already says the same thing: describing those makes a screen reader stop to announce noise. The accessible markup for a decorative image is an empty alt attribute, alt="", which the W3C documents as technique H67. It is a deliberate instruction: skip this.

A decorative image is not the same as an image with no alt. Leave the attribute off and assistive technology is left guessing, which is how file names end up read aloud. Some ranking pages say decorative images "don't need" alt text, which is true of the description and wrong about the attribute. The attribute stays; its value is empty.

That is why this checker reports only a missing attribute as a fail. A checker that flags every alt="" punishes the correct markup, and trains site owners to stuff descriptions onto dividers to make a warning go away. The cost of getting it right is the other half: an informative image someone marked alt="", a chart or a product photo, passes here, because presence is what a machine can check and meaning is what a person has to.

Writing alt text that describes

Describe what the image shows and why it is on this page. The same photograph of a building is "Front entrance of the firm's office" on a contact page and "Three-story garden apartment building, 1980s brick" in an article about property age. Context decides.

• Describe, don't stuff. Google's guidance says to avoid filling alt attributes with keywords, because it makes a poor experience and may cause the site to be seen as spam. Alt text is not a place to repeat the target phrase; it is a place to say what is in the picture.
• About a sentence. There is no official length. The working habit is one short sentence that carries the point; if the image needs a paragraph, the paragraph belongs in the page, where everyone can read it.
• Skip "image of". Screen readers already announce that there is an image. Start with the subject.
• Linked images describe the destination. When an image is the only content of a link, its alt text is the link's name. A logo linking home is "Home", or the firm's name, not a description of the logo's colors.
• Text in an image is the alt text. If an image is a quote card or a banner with words in it, the words go in the alt attribute, or better, in real text on the page.

Caption, alt text and title are three different things

A caption (<figcaption>) is visible to everyone and usually adds context the image can't: a date, a source, a credit. Alt text replaces the image for someone who can't see it. The title attribute shows as a hover tooltip, is unreliable on touch screens and is not a substitute for alt. When a caption already describes the image fully, the alt text can be short, but it should not simply repeat the caption word for word, or a screen reader user hears it twice.

Charts, screenshots and infographics

These are the images that most need real alt text and most often get a file name. A chart's alt text should say what the chart is and what it shows at the level the page relies on: "Bar chart of quarterly distributions, 2021 to 2025, detailed in the table below." A screenshot's alt text says what the screenshot demonstrates, not every pixel. When the data matter, put them in a table or in the prose next to the chart, and let the alt text point there.

For a regulated firm there is a second reason to be careful here. Alt text is content. If a chart shows performance figures, alt text that restates those figures carries the claim to screen readers and to every crawler reading the HTML, without the footnote or disclosure that sits beside the chart on screen. Describe the chart's subject and point to the table, rather than repeating its numbers, unless the disclosure travels with them. Treat alt text on any chart of returns, outcomes or results as copy, and review it with compliance the way you review the caption.

Images an alt checker can't see

Every alt checker that reads HTML shares one blind spot, and it is worth knowing where it is.

• CSS background images. A hero set with background-image has no alt attribute to check. Google's guidance says plainly that it doesn't index CSS images. If a background image carries meaning, it should be an <img>, or its meaning should be in the text on top of it.
• Inline SVG. An icon or chart drawn as <svg> takes its accessible name from a <title> inside it or from role="img" with aria-label. This checker drops SVG before it counts, so it neither passes nor fails them.
• Images added by JavaScript. A gallery or slider that inserts its images after the page loads is invisible to a tool that reads the served HTML. Check those in the browser's accessibility inspector.
• Images labelled with ARIA. An <img> named with aria-label can be accessible without an alt attribute. This checker reads only alt, so it counts that image as missing. Adding the same text as alt resolves it.

How to add alt text in your CMS

WordPress. In the block editor, select the image and fill in the Alternative text field in the block settings sidebar. Alt text set in the Media Library is copied in when the image is inserted, so editing it in the library later does not change posts that already use the image; fix each post. Leave the field empty for a decorative image and WordPress writes alt="". Static sites and templates. Add the attribute in the HTML or the template that renders the image; one missing alt in a shared template repeats on every page that uses it. Other site builders put an alt field in the image's settings panel; look for it before you publish, not after.

Why firms with something to lose check this first

Missing alternative text is one of the most common failures that WebAIM's annual Million report detects when it scans home pages, and it is among the easiest for any automated scan to find. Law firms, medical practices and other professional practices receive web accessibility demand letters, and a scan that turns up images with no alt text is an easy exhibit. Fixing missing alt text removes that finding. It does not make a site accessible on its own: color contrast, form labels, keyboard access and the quality of the alt text itself all need a person. Use this check as the first pass, and an accessibility review as the second.

Common mistakes

• File names as alt text. alt="IMG_4471" or alt="hero-final-v2" passes a presence check and helps no one.
• Descriptions on decorative images. "Decorative green line" read aloud between every section. Decorative means alt="".
• Empty alt on an image that matters. The opposite mistake, and the one no presence check catches: a chart or a team photo marked decorative, so it is silently skipped.
• The same alt on every image. A page whose twelve photos all read "our property" gives a screen reader user twelve identical, useless announcements.
• Keywords in place of a description. "Real estate syndication passive investing multifamily" is not what the photo shows, and Google's guidance names it as a spam risk.
• Performance figures in a chart's alt text with no disclosure beside them. The claim travels; the footnote doesn't.