What Is Alt Text?
Alt text (alternative text) is a short written description of an image, added in a webpage's HTML so screen readers can read it aloud and search engines can understand what the image shows. It appears in place of the image when a file fails to load. Good alt text describes an image's content and purpose in plain language, supporting both accessibility for blind and low-vision users and image SEO.
- HTML attribute
- alt="" on the <img> tag (W3C HTML spec)
- Recommended length
- About 125 characters or fewer (screen-reader convention)
- Legal relevance
- Cited in ADA/WCAG web accessibility claims (WCAG 2.1 SC 1.1.1)
- SEO role
- Primary text signal Google uses for image ranking (Google Search Central)
What does alt text actually do? #
Alt text serves three audiences at once. First, it helps people who use screen readers: assistive software reads the alt attribute aloud, so a blind user hears "Licensed plumber replacing a water heater in a Denver basement" instead of skipping past a nameless graphic. Second, it acts as a fallback for everyone, if an image file is missing, broken, or blocked by a slow connection, the browser displays the alt text where the picture should be. Third, it gives search engines a plain-language description they can index, since crawlers cannot reliably interpret the contents of a photo on their own. That last point is why alt text matters for image SEO and for appearing in Google Images. In practice, a single sentence carries a lot of weight: it can be the difference between an accessible, discoverable page and one that quietly excludes users and search bots. When we build sites, our team treats alt text as part of the content, not an afterthought bolted on before launch. You can review our approach on /services/web-design and check your own pages with /tools/ada-compliance-checker.
How do you write good alt text? #
Describe what the image shows and why it is on the page, in plain, specific language. Skip phrases like "image of" or "picture of", screen readers already announce that an element is an image. Aim for roughly one sentence, usually under about 125 characters, because many screen readers pause or truncate longer strings. Include relevant detail a sighted reader would notice at a glance: the subject, the action, and context that matters for the page. For a roofing company, "Crew installing asphalt shingles on a two-story home" beats "roof." If the image contains text, such as a promotional banner, put that text in the alt attribute so nobody misses the message. Match the description to the surrounding content: the same photo of a storefront might be described differently on an about page than in a blog post. Avoid keyword stuffing, cramming in search terms reads as spam to both users and Google. Write for a listener first, and the SEO benefit follows naturally. For local businesses, see examples on /web-design-for-roofers and /web-design-for-dentists.
When should an image have empty alt text? #
Not every image needs a description. Purely decorative graphics, background flourishes, divider lines, spacer images, or an icon that merely repeats adjacent text, should carry an empty alt attribute written as alt="" (with nothing between the quotes). This tells screen readers to skip the image entirely rather than announcing a distracting or redundant string. Leaving the attribute off completely is different and worse: some screen readers will then read the image file name aloud, so a user hears "IMG underscore 4021 dot jpg," which helps no one. The rule of thumb is to ask whether the image adds information. If a decorative swirl were removed, would a user lose any meaning? If not, empty alt is correct. If the image conveys content, a chart, a product photo, a team headshot with a caption, it needs a real description. Functional images, like a logo that links to the homepage, should describe the function: "LocalWebAdvisor home." Getting this distinction right is a core part of WCAG compliance; learn more at /wiki/what-is-ada-website-compliance.
How does alt text affect SEO? #
Search engines read alt text as a strong signal of what an image depicts, which influences whether that image ranks in Google Images and how well the whole page matches a query. Because Google cannot fully "see" a photo, the alt attribute, along with the file name, caption, and surrounding text, tells it the subject. Descriptive alt text can drive image search traffic, which matters for visual industries like restaurants, salons, and contractors where people search for pictures. It also reinforces the page's topical relevance. That said, alt text is not a place to dump keywords; Google's guidelines explicitly warn against overstuffing, and doing so can look manipulative. Write natural descriptions that happen to include the terms real people use, and you get accessibility and ranking benefits together. Alt text is one piece of a broader image and page optimization strategy that also includes compressed file sizes and fast load times, both covered on /services/speed-optimization and in /wiki/website-speed-guide. For a full local strategy, see /services/local-seo and /wiki/what-is-local-seo.
Where does alt text live in the code? #
Alt text is an attribute on the HTML image tag. Every content image should include it. Content management systems like WordPress expose an "alt text" field in the media library so you rarely touch code directly, but it is worth understanding what gets written behind the scenes. When the attribute is present and populated, screen readers and crawlers use it. When it is present but empty, decorative images are skipped cleanly. When it is missing entirely, tools flag an accessibility error. Page builders, themes, and ecommerce platforms sometimes strip or auto-generate alt attributes, so it pays to audit after any redesign or migration, which is exactly the kind of thing we check on /services/website-migrations and /services/wordpress-development. If you manage a large catalog, editing alt text image by image is tedious but important, especially for product photos that drive both accessibility and image search visibility.
What are common alt text mistakes? #
The most frequent error is leaving alt text off entirely, which fails accessibility checks and wastes an SEO opportunity. Close behind is keyword stuffing, packing the attribute with repeated search phrases that read as spam and can harm rankings. Another mistake is redundancy: describing an image whose caption already says the same thing, forcing screen-reader users to hear it twice. Writing "image of" or "photo of" at the start is unnecessary noise. Auto-generated alt text from a CMS or AI tool is a starting point, not a finished product, generic outputs like "a group of people" miss the context that makes a description useful. Overly long alt text that runs to several sentences frustrates screen-reader users; if an image genuinely needs a long explanation, such as a complex infographic, provide that detail in nearby body text or a linked long description and keep the alt short. Finally, using the same alt text on every image on a page tells search engines nothing distinct. Run a scan with /tools/ada-compliance-checker to catch these quickly.
How does alt text relate to ADA compliance? #
Providing text alternatives for images is one of the most fundamental requirements of web accessibility. The Web Content Accessibility Guidelines (WCAG), the standard US courts and the Department of Justice point to when evaluating ADA claims, list "non-text content" needing a text alternative as Success Criterion 1.1.1, at the baseline Level A. In plain terms, that means images must have appropriate alt text (or empty alt if decorative) to meet the lowest bar of accessibility. Businesses have faced demand letters and lawsuits over inaccessible websites, and missing alt text is among the easiest violations for a plaintiff's tool to detect. For local service businesses, an accessible site is both a legal safeguard and a way to serve more customers, including the millions of Americans who rely on screen readers. Alt text alone does not make a site compliant, but a site cannot be compliant without it. We build accessibility in from the start on /services/web-design and offer ongoing checks through /services/care-plans. Learn the full picture at /wiki/what-is-ada-website-compliance.
Does alt text work for logos, icons, and buttons? #
Yes, but the description should reflect the image's function rather than its appearance. A logo that links to the homepage should have alt text like "Acme Plumbing home," because to a screen-reader user it works as a navigation link, not a decorative graphic. An icon that stands alone as a button, say a magnifying glass that triggers search, needs alt text such as "Search" so the control is usable without sight. If the same icon sits beside a visible text label that already says "Search," the icon is decorative and should get empty alt to avoid the label being read twice. Social media icons should name the destination: "Follow us on Facebook." The guiding question for any functional image is: what would a sighted user understand this element does, and how do I convey that in a few words? Getting these small labels right is part of thoughtful interface work, which we cover on /services/ui-ux-design and /services/conversion-optimization.
FAQ
How long should alt text be?
Aim for a single descriptive sentence, generally under about 125 characters. Many screen readers pause or cut off longer strings, so brevity keeps the description usable. If an image genuinely needs a longer explanation, like a detailed chart, keep the alt short and put the full detail in nearby body text or a linked long description.
Do decorative images need alt text?
Decorative images should have an empty alt attribute, written as alt="" with nothing inside. This tells screen readers to skip the image so users are not distracted by meaningless descriptions. Leaving the attribute off entirely is worse, because some screen readers will then read the file name aloud instead.
Is alt text a Google ranking factor?
Alt text helps images rank in Google Images and reinforces a page's topical relevance, so it contributes to SEO. Google reads it as a primary signal of what an image shows. Write natural, accurate descriptions rather than stuffing keywords, which Google's guidelines warn against and which can hurt your rankings.
What happens if I forget alt text?
The image still displays, but screen-reader users get no description (or hear the file name), your page can fail accessibility and WCAG checks, and you miss image-search traffic. Missing alt text is one of the most common issues flagged in ADA-related website complaints, so it is worth auditing regularly.
Should alt text include my keywords?
Include keywords only when they naturally describe the image. If a photo shows a plumber fixing a water heater, writing that is both accurate and keyword-relevant. Forcing unrelated search terms in is keyword stuffing, which reads as spam to Google and screen-reader users alike and can damage rankings.
Can AI or my CMS write alt text automatically?
Auto-generated alt text is a helpful starting point but rarely finished. Tools often produce generic descriptions like "a group of people" that miss the context making a caption useful. Review and edit auto-generated alt text so it accurately reflects the image and its purpose on the specific page where it appears.
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