What is Alt Text in SEO?

Q: What happens if I leave out the alt attribute vs. writing alt=""?

If you write alt="" (an empty null attribute), screen readers recognize the image as purely decorative and skip over it smoothly. If you omit the alt attribute entirely ( ), screen readers assume the developer forgot to make the image accessible and read the raw image URL or filename aloud to the user.

Q: Should I put alt text on background images loaded via CSS (background-image)?

CSS background-image properties do not support alt attributes and are ignored by both screen readers and Google Images. Only use CSS background images for purely decorative textures or gradients; any informative product screenshot, chart, or diagram must use an HTML tag.

Reviewed by Sitab Ahamed 7 min read

Quick Definition

Alt text (short for alternative text, also known as the HTML alt attribute) is a concise written description embedded inside an HTML <img> tag that describes the appearance, function, or data of an image on a webpage. Formally specified in the W3C HTML Living Standard and mandated by WCAG 2.1 Success Criterion 1.1.1, alt text serves three critical roles: reading visual content aloud to blind and low-vision screen reader users, displaying fallback text when an image fails to load, and providing explicit semantic context to Google Images, Google Lens, and multimodal AI search engines.

HTML Syntax <img src="chart.webp" alt="Descriptive text">

Linked Image Rule Google treats the alt text of a linked <a><img></a> as Anchor Text

Decorative Image Rule Use empty null alt="" (Never omit the alt attribute entirely)

What is Alt Text? (HTML Syntax & How Crawlers Read It)

In HTML markup, the alt attribute resides directly inside the image element:

<img src="/assets/images/b2b-saas-seo-buyer-journey-funnel.webp" alt="B2B SaaS SEO buyer journey funnel showing TOFU, MOFU, and BOFU conversion stages" width="800" height="450">

According to Google Search Central’s Google Images Best Practices documentation, Google extracts information about the subject matter of an image from the image’s alt text, combined with computer vision algorithms and the surrounding page headings and captions. Furthermore, whenever an image is wrapped inside an HTML hyperlink (<a href="/pricing"><img src="..." alt="Enterprise SaaS Pricing Plans"></a>), Googlebot uses the image’s alt text exactly like standard hyperlink anchor text to understand the destination URL!

Good vs. Bad Alt Text Examples (Avoiding Keyword Stuffing)

Google explicitly warns in its Search Essentials guidelines that filling alt attributes with lists of keywords ("keyword stuffing") results in a negative user experience and can cause your site to be flagged by spam classifiers. Compare how different alt attributes perform for a B2B SaaS dashboard screenshot:

Alt Text Quality Tier	HTML Code Example	Why It Fails or Succeeds
Missing Alt Attribute (Worst)	`<img src="IMG_4092.webp">`	Fails ADA / WCAG 1.1.1. Screen readers read the raw filename ("I-M-G underscore four zero nine two dot webp") aloud!
Keyword-Stuffed (Spam Risk)	`<img src="gsc.webp" alt="B2B SaaS SEO agency best SaaS SEO consultant SEO services">`	Violates Google Spam Policies. Unusable for visually impaired users and ignored or demoted by Google Images.
Generic / Lazy (Weak)	`<img src="gsc.webp" alt="image of chart">`	Zero Information Gain. Also wastes characters on "image of" (screen readers already announce "Graphic" or "Image" automatically).
Descriptive & Specific (10x Best Practice)	`<img src="gsc.webp" alt="Google Search Console performance graph showing organic clicks growing from 12,000 to 181,000 over 12 months">`	Optimal for Accessibility, Google Images & AEO. Conveys the exact data insight of the chart in natural language.

Technical Edge Cases: Decorative Images (alt="") & Inline SVGs

Not every visual file on a webpage should have descriptive text. Applying the W3C decision tree prevents assistive technology clutter:

Purely Decorative UI Graphics (Must Use alt=""): Background gradients, divider lines, abstract decorative blobs, and icons placed right next to text labels that already state the exact same word (e.g., a magnifying glass icon inside a button that already says Search) must have an empty null attribute (alt=""). An empty alt="" instructs screen readers to skip the element silently, whereas omitting alt altogether is a WCAG error.
Inline <svg> Elements: Because inline <svg> tags do not support the HTML alt attribute, decorative SVGs should include aria-hidden="true", while informative SVG diagrams should include role="img" and an internal <title> element referenced via aria-labelledby.
Complex Infographics & Architecture Diagrams: When embedding a detailed B2B system architecture diagram or data chart, summarize the core conclusion in the alt attribute (under ~125-150 characters) and provide the full data breakdown in an adjacent HTML table or <figcaption> so both screen readers and LLM crawlers can extract every data point.

The Complete B2B SaaS Image SEO & Multimodal Checklist

How to Rank SaaS Product Screenshots & Charts in Google Images

1. Pair Descriptive Filenames with Contextual Alt Text: Before uploading, rename Screenshot-2026-10-17.png to b2b-saas-technical-seo-case-study-181k-clicks.webp. Google Search Central confirms that descriptive, hyphen-separated filenames reinforce your alt attribute.

2. Eliminate "Image of" and "Picture of" Prefixes: Screen readers like VoiceOver and NVDA automatically announce "Image:" before reading your alt string. Writing alt="Image of a funnel" causes the user to hear "Image: Image of a funnel." Jump straight into describing the content.

3. Include All Key Images in Your Dedicated Image Sitemap: List your product diagrams, case study charts, and frameworks in /image-sitemap.xml so Googlebot discovers even images loaded inside interactive components.

Frequently Asked Questions

Is there a strict 125-character limit for alt text?

There is no hard character limit in the HTML specification or in Googlebot’s parser. The popular "125-character rule" originated from older versions of the JAWS screen reader, which used to pause or split announcements after 125 characters. While modern screen readers can read longer strings, keeping alt text concise (typically 8 to 20 words, or under ~125-150 characters) remains the best practice for usability.

What happens if I leave out the alt attribute vs. writing alt=""?

If you write alt="" (an empty null attribute), screen readers recognize the image as purely decorative and skip over it smoothly. If you omit the alt attribute entirely (<img src="banner.webp">), screen readers assume the developer forgot to make the image accessible and read the raw image URL or filename aloud to the user.

Does alt text help my webpage rank higher in regular web search or just Google Images?

Both! While alt text is one of the strongest signals for ranking in Google Images and Google Discover, Google also renders visual thumbnails next to standard mobile web search snippets and uses image alt text to reinforce the topical completeness of your article, plus uses it as anchor text whenever an image is hyperlinked.

Should I put alt text on background images loaded via CSS (background-image)?

CSS background-image properties do not support alt attributes and are ignored by both screen readers and Google Images. Only use CSS background images for purely decorative textures or gradients; any informative product screenshot, chart, or diagram must use an HTML <img> tag.