Image Alt Text Writing
Alt text is the one on-page element with a legal accessibility requirement attached, and most sites leave it empty. Ivan Sp writes alt text aimed at someone who genuinely cannot see the image, not as a place to stuff extra keywords. The dual purpose is deliberate. Real accessibility for screen reader users and one of Google’s oldest, most reliable image signals get earned the same way at the same time.
Semantic Triples, Not Keyword Strings
Every alt text follows a subject-verb-object structure in active voice, describing what the image actually shows rather than listing terms associated with the page. “Dentist examines patient teeth with dental mirror” describes a scene. “Dentist, dental exam, teeth cleaning, Edmonton dentist” describes nothing, and reads as exactly the stuffing pattern quality systems are built to catch.
The main entity of the page appears in the alt text where the image genuinely relates to it. The same canonical name gets used everywhere else on the page, rather than a synonym chosen for variety.
Batch Generation to a Fixed Specification
Location page sets and product catalogues generate alt text at volume against a strict specification, rather than reviewed one image at a time. One batch produced 200 image alt text attributes built around a city variable, each written to a fixed rule covering length, sentence structure, and a list of excluded commercial words.
The specification exists precisely so a generator cannot drift toward keyword stuffing at scale. A rule enforced on one image is easy to check by eye. A rule enforced on 200 images needs to be written down first.
Accessibility Comes First, SEO Follows
I write alt text for a person using a screen reader first, then evaluates it as an SEO asset. An image conveying no real information, such as a decorative divider, gets an empty alt attribute rather than a forced description invented to fill the field.
Writing a description a sighted reader would never think to write, purely because the field exists, produces text that helps neither audience it was meant to serve.
Pronoun-Free, Plain-Language Writing
I avoid pronouns in alt text. An image has no antecedent for “it” or “they” once a screen reader announces the description with no surrounding context. Genuine synonyms of the main entity are fine, and a vague substitute that loses the entity’s identity is not.
Reading level stays around a sixth-grade standard, with technical terms kept only where they are genuinely necessary to describe what the image shows accurately.
Alt Text Compared to Filename Optimization
Alt text describes the image in a sentence. Filenames carry a separate, shorter signal, covered under image optimization for filenames, formats, and compression. Both apply to the same image and serve related but distinct purposes.
Where the Standard Alt Text Advice Breaks Down
- The usual advice
- Add alt text to every image, and include the page’s target keyword in each one.
- What holds up in practice
- Not every image should have alt text at all. A decorative image needs an empty alt attribute, and describing it forces a screen reader to announce something with no informational value.
Consider a site that adds descriptive alt text to all 340 images, including every divider, icon, and background flourish. Every accessibility checker reports full coverage.
A person using a screen reader now hears a description of a decorative line between each section. Coverage went up, and the page became harder to listen to.
I classify before writing. Meaningful images get one plain sentence, and decorative images get an empty attribute that tells the screen reader to move on.
Treating alt text as a coverage metric makes the page worse for the exact audience the requirement exists to protect.
Four Things Commonly Assumed About Alt Text
Have you ever listened to one of your own pages through a screen reader?
Ivan Sp meets these four assumptions whenever alt text is treated as a coverage metric.
| Commonly assumed | What actually holds |
|---|---|
| Alt text is an SEO field. | Alt text exists to satisfy an accessibility requirement, WCAG success criterion 1.1.1. Search benefit follows from doing that properly. |
| Full alt text coverage is the goal. | Decorative images should carry an empty alt attribute. Describing every divider makes a page worse to listen to. |
| Missing and empty alt attributes are the same thing. | A missing attribute makes a screen reader announce the filename. An empty one tells it to skip the image entirely. |
| Alt text should start with the words image of. | A screen reader already announces that an image is present. The words are pure redundancy in every description. |
| Longer alt text is more descriptive. | One sentence under roughly 125 characters is usually right. Longer descriptions belong in a caption where sighted readers benefit too. |
Treating alt text as a coverage metric makes the page worse for the exact audience the requirement exists to protect. It also happens to be the version search engines read.
Alt Text Reference
- Governing standard
- WCAG 2.1 success criterion 1.1.1, Non-text Content, at conformance level A.
- Primary audience
- People using screen readers, who hear the alt text in place of the image.
- Decorative images
- Should carry an empty alt attribute, which tells a screen reader to skip them.
- Missing versus empty
- A missing attribute makes a screen reader read the filename aloud. An empty one does not.
- Recommended form
- One plain sentence in active voice describing what the image shows.
- What to avoid
- Keyword lists, the phrase image of, and pronouns with no antecedent.
- Functional images
- A linked image needs alt text describing the destination rather than the picture.
A Worked Example: Four Alt Texts for One Photograph
Consider a photograph of a technician servicing a rooftop unit. The four versions below are illustrative, written to show what each rule changes. None is taken from a client engagement.
| Version | Alt text | Assessment |
|---|---|---|
| Missing | No alt attribute at all | A screen reader announces the filename instead |
| Keyword stuffed | hvac repair vancouver hvac service commercial hvac | Unreadable aloud, and no description of the image |
| Vague | Image of a worker | Accurate and uninformative, and the words image of are redundant |
| Written to spec | A technician replacing a compressor on a rooftop air conditioning unit | Describes the subject in one sentence, in active voice |
I write the fourth version by describing what is visible and stopping. The subject, the action, and the object are all present, and no keyword is forced in.
Alt text works like describing a photograph over the phone. Nobody reads a list of nouns aloud, and one clear sentence lands immediately.
The fourth version happens to contain the relevant terms. The terms arrived because the image genuinely shows that work, which is the only reason they belong.
How Alt Text Gets Written
I write alt text to a fixed specification, whether for nine images or nine hundred.
- Crawl the site and export every image with its current alt attribute and its containing URL.
- Split the export into meaningful images, decorative images, and images used as links.
- Set an empty alt attribute on every decorative image, rather than deleting the attribute.
- Write one active-voice sentence per meaningful image, naming subject, action, and object.
- Describe the destination rather than the picture wherever an image is wrapped in a link.
- Remove the phrase image of, remove pronouns, and remove any keyword the image does not show.
- Keep each description under roughly 125 characters, which most screen readers handle in one breath.
- Batch product and location images against a template that varies by the real attributes of each item.
- Re-crawl after deployment, and confirm no meaningful image is left with a missing attribute.
How This Work Is Scoped
I scope alt text work by image count, and by whether the set is templated or individual.
- What arrives
- A spreadsheet mapping every image URL to its written alt text, ready for import.
- Typical duration
- Three to seven working days for a set of five hundred images.
- What the client supplies
- Media library access, and product attribute data where images are catalogue items.
- Included
- Audit, classification, writing, batch generation for templated sets, and a verification crawl.
- Not included
- Full accessibility auditing beyond images, and remediation of other WCAG criteria.
- What changes the estimate
- Sets above roughly five thousand images, or images with no usable attribute data.
- How it is quoted
- After a short scoping call, once image count and platform are known.
Tools and Primary Sources
The references below define the requirement and the guidance. Each opens in a new tab.
- WCAG 2.1 non-text content is the accessibility criterion alt text exists to satisfy.
- W3C alt decision tree walks through which images need description and which should be marked decorative.
- Google image SEO guidance sets out how Google uses alt text and what counts as over-optimisation.
- Screaming Frog SEO Spider exports every image with its alt attribute, which makes missing values countable.
Hear Your Own Page
I suggest a check that reveals the problem faster than any report.
- Open your most important page in a browser.
- Turn on the screen reader built into your operating system.
- Listen to the page from the first heading through to the first three images.
- Note every point where a filename or a keyword list is read aloud.
Hearing a filename read out is the clearest evidence of a missing attribute. Hearing a keyword list is evidence of alt text written for the wrong audience.
Common Questions
Does every image need alt text?
Every meaningful image needs alt text. Purely decorative images, such as spacing dividers with no informational content, get an empty alt attribute instead of a forced description.
How long should alt text be?
Roughly 8 to 15 words is typical, enough to describe the image accurately without turning into a full paragraph. Length follows what the image actually needs to be described, not a fixed target.
Can alt text alone improve image search rankings?
Alt text helps, alongside filename, surrounding context, and technical image factors such as format and compression. No single element carries the full weight, and alt text works as one signal among several rather than in isolation.
How long should alt text be?
One sentence is usually right, and roughly 125 characters is a practical ceiling. Longer descriptions belong in a caption or in the body copy, where sighted readers can also benefit.
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