Alt text (alternative text) is the value of the HTML alt attribute on an img element. It's a written description of what the image shows. Screen readers read it out loud, search engines use it to understand and rank images, and AI assistants like ChatGPT and Perplexity use it to decide whether to cite your page when answering visual queries. If the alt text is missing, all three are guessing — usually wrong.

What is the difference between alt text and a caption?

Alt text lives inside the HTML and is invisible to sighted users — it's read aloud by screen readers and parsed by search engines. A caption is visible text that sits next to the image, usually in a figcaption element. Both can describe the same image, but they serve different audiences: alt text serves accessibility and SEO; captions serve sighted readers who want context. Use both when the image needs both.

What is the difference between alt text and the title attribute?

The alt attribute is required and screen readers always read it. The title attribute is optional, shows on hover, and is unreliable on mobile and inconsistently surfaced by screen readers. Use alt for accessibility and SEO. Skip title unless you have a specific reason — it usually adds noise without value.

Is it 'alt text' or 'alt-text'?

Both spellings are equally common in writing. The HTML attribute itself is just alt (no hyphen). 'Alt text' (two words, no hyphen) is the form Google, W3C, and most accessibility documentation use, so we use it on this site too. 'Alt-text' (hyphenated) means the same thing — don't worry about it.

Should it be 'alt text' or 'alt texts' for multiple images?

'Alt text' works as both singular and plural collective noun — like 'feedback' or 'hardware.' You can say 'alt text for 1,000 images' and it's fine. 'Alt texts' (plural) is also valid when you're talking about several distinct descriptions side by side. Either is correct.

What is the difference between alt text and alt description?

They're the same thing. The HTML attribute is alt, and people refer to its value interchangeably as alt text, alt description, alt attribute, or alt tag. There's no functional difference — just preference. We use 'alt text' throughout AltText.ai because it's the most common phrasing.

What about 'alt image'?

'Alt image' is a casual phrasing that usually means the alt text on an image — the alt attribute value. There's no separate concept called 'alt image' in HTML or accessibility specs. If you're searching for help with 'alt image,' you almost certainly want help with alt text.

What is alternative text?

Alternative text is the long form of alt text. The HTML attribute name is short for 'alternative text' — meaning text that serves as an alternative when the image can't be seen or rendered. The terms are interchangeable; specs and accessibility documentation use 'alternative text,' while developers usually shorten it to 'alt text.'

What is an altgenerator (alt generator)?

An alt generator (sometimes written 'altgenerator' as one word) is a tool that automatically writes alt text for images. AltText.ai is an alt generator — it scans your images and produces SEO-aware, accessibility-compliant descriptions in 130+ languages, then writes them back to your CMS. Use it when you have more images than you can describe by hand, which is most websites past the first 100 photos.

How long should alt text be?

Aim for 80 to 140 characters. Under 80 is usually too sparse to be useful for screen reader users; over 140 starts cluttering the audio experience. Specific exceptions exist — charts and infographics often need longer alt text or a separate long description — but for product photos, hero images, and editorial photography, 80–140 is the sweet spot.

Accessibility · SEO · AI Search

What Is Alt Text? The Complete 2026 Guide

The HTML attribute that decides whether your images are visible to screen readers, search engines, and AI assistants — or invisible to all three.

April 28, 2026 · 11 min read

Alt text is the descriptive value of the HTML alt attribute on an image. It's a written sentence that explains what the picture shows. Three audiences read it: screen readers (out loud, for users who can't see the image), search engines (to understand what the image depicts and rank it accordingly), and AI search assistants like ChatGPT, Claude, and Perplexity (to decide whether to cite your page when someone asks them a visual question).

If your alt text is missing, vague, or stuffed with keywords, all three audiences fail — and you lose the traffic, accessibility compliance, and AI visibility that good alt text earns. This guide explains exactly what alt text is, why each audience matters, how to write alt text that works for all three, and the most common mistakes that quietly cost you rankings.

Key Takeaways

Alt text is the value of the HTML alt attribute. It describes the image to anyone or anything that can't see it.
Write 80–140 characters. Skip "image of" and "picture of" — the screen reader already announces it as an image.
Decorative images use empty alt (alt=""), not missing alt. Missing alt makes screen readers read the filename out loud.
Alt text is now an AI search ranking signal, not just an SEO one. ChatGPT, Claude, and Perplexity all use it to understand product images.
For sites with more than 100 images, automate it. Manual alt text doesn't scale, and inconsistent quality is worse than no policy at all.

What Is Alt Text? (The Full Definition)

In HTML, every image element looks like this:

<img src="golden-retriever.jpg" alt="A golden retriever returning a tennis ball at a sunny park">

The alt attribute is the alt text. It's mandatory under the HTML spec — every <img> must have one, even if it's empty. The value can be a sentence, a phrase, or an empty string (alt="") for decorative images. The W3C's Web Accessibility Tutorials are the canonical reference for what counts as good alt text and when to leave it empty.

"Alt" stands for "alternative." The full name is alternative text: text that serves as an alternative when the image can't be perceived. That covers four scenarios: a screen reader user, an image that fails to load, a slow connection that hasn't downloaded the image yet, and a search engine or AI assistant that can't interpret the pixels directly.

Why Alt Text Matters

1. Accessibility (and Legal Compliance)

Roughly 1 in 5 adults in the U.S. lives with a disability that affects how they use the web, according to the CDC. Many use screen readers — software like JAWS, NVDA, and VoiceOver that reads the page out loud. When the screen reader reaches an image, it reads the alt text. If the alt text is missing, it reads the filename. "I-M-G underscore zero zero zero seven dot J-P-G" is not a useful sentence.

Beyond user experience, alt text is a legal requirement in many jurisdictions. WCAG 2.2 Success Criterion 1.1.1 requires text alternatives for all non-text content. ADA web accessibility guidance uses WCAG as its reference standard, and U.S. federal courts have been ruling against companies for inaccessible websites for over a decade. Missing alt text is one of the easiest violations for an automated audit to flag.

2. SEO (Image Search and Page Rankings)

Google explicitly states in its Google Images guidelines that alt text is a primary signal for understanding what an image shows. That matters for two reasons. First, your images can rank in Google Images and drive their own organic traffic — Google Images accounts for roughly a quarter of all Google searches across the web, and far higher for visual industries like apparel, recipes, and home goods. Second, alt text strengthens the topical relevance of the page itself. A product page with descriptive alt text on every product photo sends Google a clearer signal about what the page is about than the same page with empty alts.

For deeper SEO mechanics — keyword placement, length sweet spots, and the rules that have changed since 2018 — see our companion guide: Alt Text for SEO in 2026: 9 Rules That Move Rankings.

3. AI Search Visibility

This is the angle that's changed most rapidly. ChatGPT, Claude, Perplexity, and Google's AI Overviews don't browse the web the way a human does. When they answer a visual query — "show me a credenza that fits under a window" — they cite pages whose images are richly described in machine-readable text. They read alt text. They read schema. They read the surrounding paragraph. If your product images have empty alts and your competitor's don't, the AI cites your competitor.

This is the part of alt text that didn't exist five years ago. AI assistants are now a meaningful traffic source for ecommerce, content sites, and marketplaces, and they're disproportionately reliant on textual descriptions of images because they don't actually look at pixels in the same way Google Image Search does. Alt text is the cheapest way to make sure your products are visible to them.

How to Write Good Alt Text

Five rules cover 95% of alt text writing:

Describe what's in the image, in context. The same photo on a coffee shop site versus a pottery blog needs different alt text — context decides what's relevant.
Be specific. "Golden retriever returning a tennis ball at a sunny park" beats "dog playing." Specificity is what makes alt text useful.
Skip "image of" and "picture of." Screen readers already announce that they're reading an image. Adding "image of" wastes characters and irritates the listener.
Aim for 80–140 characters. Long enough to be useful, short enough to keep the audio experience flowing.
Use empty alt for decorative images. If removing the image wouldn't change the page's meaning, set alt="". Don't omit the attribute — that makes screen readers fall back to the filename.

10+ Before-and-After Examples

The clearest way to learn alt text is to see bad, okay, and good versions side by side. The pattern is the same every time: bad alt text is generic or filename-based; okay alt text describes the subject; good alt text describes the subject and the context that matters for the page.

Product photo on an ecommerce site

Bad: "product1.jpg"
Okay: "Blue running shoe"
Good: "Men's Nike Pegasus 41 in royal blue, side view, with white midsole"

Bar chart in a blog post

Bad: "chart"
Okay: "Bar chart of monthly revenue"
Good: "Bar chart: Product A revenue grew from $10K in January to $20K in June; Product B steady at $12K; Product C declined from $15K to $8K"

Decorative texture in a page background

Bad: "background.png"
Okay: "Background pattern" (still announces a non-essential element)
Good: alt="" (screen reader skips it cleanly)

Team photo on an About page

Bad: "team"
Okay: "AltText.ai team"
Good: "The AltText.ai team standing in front of the office whiteboard, eight people, casual attire"

Recipe photo on a food blog

Bad: "recipe"
Okay: "Pasta dish"
Good: "Bowl of cacio e pepe pasta with cracked black pepper and shaved pecorino, served on a white linen napkin"

Logo that links to the homepage

Bad: "logo.svg"
Okay: "Company logo"
Good: "AltText.ai home" (describes the link's destination, not the visual)

Icon paired with a visible text label

Bad: "icon" alongside the word "Settings"
Good: alt="" — the visible "Settings" label already announces the function; alt would be redundant

Infographic with multiple data points

Bad: "infographic"
Good: Short alt text summarizing the headline finding ("Infographic: AI search referrals grew 4x year-over-year") plus a long description in surrounding text or a linked transcript page

Meme or stylized image

Bad: "funny image"
Good: Describe the image AND transcribe the text overlay: "Distracted boyfriend meme: man labeled 'me' looks back at woman labeled 'shiny new framework' while ignoring his date labeled 'the codebase that pays the bills'"

Screenshot of a software interface

Bad: "screenshot.png"
Good: "Shopify product editor with the AltText.ai panel showing auto-generated descriptions for 12 product images"

Common Alt Text Mistakes

Five mistakes show up over and over in accessibility audits and SEO reviews:

Missing alt attribute entirely. Not the same as empty alt. Missing means screen readers fall back to the filename. Always include the attribute, even if you set it to "".
Keyword stuffing. "Blue shirt blue clothes blue cotton tee shirt SEO blue blue clothing." Search engines penalize it; screen reader users hate it.
Reusing the same alt text on every image. "Golden retriever" on twelve different photos of twelve different dogs makes all twelve images useless.
Starting with "image of" or "picture of." Screen readers already announce that the element is an image. The phrase wastes characters.
Treating decorative and functional images the same. Empty alt for decorative; descriptive alt for functional. When you blur the distinction, screen reader users hear noise instead of content.

For deeper coverage of mistakes specific to ecommerce and high-volume catalogs, see Common Alt Text Mistakes That Hurt Image SEO.

Length: The 80–140 Character Sweet Spot

Most reputable accessibility references converge on the same range. The WebAIM alt text guide recommends keeping alt text short enough to fit cleanly into spoken audio. The HTML spec doesn't enforce a maximum, but screen readers truncate at around 125 characters in some configurations, and many accessibility checkers flag alt text over 150 characters as too long.

The 80–140 range balances three constraints: useful enough to convey the image, short enough not to disrupt screen reader flow, and structured enough that search engines can extract a clear topic. If you genuinely need more than 140 characters — a complex chart, a detailed infographic, an instructional diagram — write a short alt text and provide a longer description in the surrounding text or a linked long-description page.

Tools to Generate Alt Text at Scale

If you have fewer than 100 images, write them by hand. Past that, manual alt text becomes the bottleneck — you ship products, blog posts, and campaigns without alt text because nobody has time, and the gap compounds. The fix is automation that produces context-aware descriptions, not generic captions.

You can scan your site for free to see how many images on your site are missing alt text right now. If the gap is large, AltText.ai generates SEO-aware, accessibility-compliant descriptions in 130+ languages and writes them back to your CMS. Pricing starts free with 25 images included, and there are direct integrations for WordPress, Shopify, and a dozen other platforms. For accessibility-focused teams, the accessibility solutions page covers WCAG audit workflows.

Next Steps

Run a free accessibility audit to see how many of your images are missing alt text.
Read Alt Text for SEO in 2026 for the rules that actually move rankings.
Read Common Alt Text Mistakes for the top errors to avoid.
If your site has thousands of images, see how automation works for WordPress, Shopify, or any platform via the API.

FAQ

The structured FAQ data above answers the questions people most often search alongside "alt text." If you have a specific question we haven't covered, send us a note via Support and we'll add it here.