Alt text
Text alternative for images, used by screen readers and search engines.
Alt text (the HTML alt attribute on an <img> tag) is a text alternative describing an image's content and function, read aloud by screen readers to users who can't see the image, and displayed in the browser if the image fails to load. It exists first and foremost as an accessibility requirement, and secondarily as an SEO signal that helps search engines understand image content since they cannot 'see' pixels the way a person does.
Well-written alt text describes both what the image shows and why it's there — a photo of a technician performing an inspection should describe the action and context, not just list objects ('man, ladder, roof'). Poorly written alt text is either empty on meaningful images (breaking accessibility) or stuffed with unrelated keywords (a spam pattern search engines actively discount).
Alt text also feeds Google Images, which drives meaningful traffic for many visual, before/after, and product-style businesses, and increasingly feeds visual-input AI systems that use alt text as a grounding signal when interpreting an image alongside surrounding page copy.
How alt text is used by search engines and assistive tech
Screen readers announce the alt text in place of the image when a user tabs or arrows to it, meaning the alt text is the entirety of what a blind or low-vision user perceives about that image — get it wrong and you've either given them nothing (empty alt on a meaningful image) or noise (a keyword string that doesn't describe anything real).
Search engines use alt text, in combination with the image filename, surrounding text, and page context, to determine relevance for Google Images and to reinforce the topical signal of the page it sits on. It is a supporting signal, not a primary ranking lever for the page's main-content rankings, but it is one of the highest-leverage, lowest-effort fixes available on most content audits because it is so frequently done poorly or skipped entirely.
Decorative vs meaningful images
A purely decorative image — a background texture, a stylistic divider — should carry an empty alt attribute (alt="") rather than no alt attribute at all, which tells screen readers to skip it silently rather than fall back to reading the filename aloud, a jarring experience ('IMG_4821 dot jpg').
A meaningful image — a product photo, a diagram, a photo illustrating a process step, a chart — needs descriptive alt text every time. The test is simple: if removing the image would remove information a sighted user relies on, it needs real alt text; if it's purely visual flourish, it needs an empty attribute.
How to write good alt text
Describe the image concisely and specifically — what's shown and, where relevant, its function (a linked logo image's alt text should describe the destination, e.g. 'Optimize Plus homepage' rather than 'logo'). Avoid starting with 'image of' or 'picture of', which screen readers already announce automatically as an image; it's redundant.
Keep it under roughly 125 characters where possible, since some screen readers truncate longer alt text, and never include a keyword that isn't genuinely descriptive of the image just to chase Google Images traffic — that pattern is easy to spot and does more harm than good.
Common mistakes
The two failure modes sit at opposite extremes: leaving alt attributes entirely empty or missing on meaningful content images (an accessibility and SEO miss), or stuffing them with unrelated keyword strings that read like spam to both users and algorithms.
- Missing alt attribute entirely on meaningful images (different from an intentionally empty alt="").
- Keyword-stuffed alt text unrelated to the actual image content.
- Filename-as-alt-text (e.g. alt="img4821.jpg"), providing zero descriptive value.
- Decorative images given verbose alt text that adds screen-reader noise for no informational gain.
Auditing alt text at scale
A full-site crawl will flag every image missing an alt attribute in seconds; the harder work is manually reviewing existing alt text for quality, since a crawler can confirm an attribute exists but can't judge whether 'photo1' is a good description. Prioritise product images, hero images, and diagrams first, since these carry the most information density and the most Google Images opportunity.
Local service-business application
Before/after photos are one of the highest-value image categories for local service businesses (roofing, landscaping, remodeling) and deserve genuinely descriptive alt text: 'Before and after photo of a re-shingled roof repair in Round Rock, TX' rather than 'roof1.jpg' — this both serves accessibility and captures a meaningful share of Google Images searches for that exact query pattern.
Team and location photos should describe context naturally ('Optimize Plus technician inspecting HVAC unit in an Austin backyard') rather than stuffing a city name into every single alt attribute on the page, which reads as manipulative and provides no additional accessibility value beyond the first accurate mention.
Alt text quick-reference
| Decorative image | alt="" | Empty, not missing — tells screen readers to skip silently. |
|---|---|---|
| Meaningful image | Descriptive, specific | Describe content and function, under ~125 characters where practical. |
| Linked image (e.g. logo) | Describe destination | 'Optimize Plus homepage', not 'logo'. |
| Keyword density | Zero tolerance for stuffing | Only include terms genuinely descriptive of the image itself. |
Frequently asked questions
- What's the difference between alt text and a title attribute on an image?
- Alt text is the accessible text alternative read by screen readers and is essential; the title attribute shows as a hover tooltip and is rarely read by assistive technology, so it should never be relied on as a substitute for proper alt text.
- Should decorative images have alt text?
- They should have an empty alt attribute (alt=""), not no attribute at all and not descriptive text. This tells screen readers to skip the image entirely rather than announce something like the raw filename, which is a worse experience than skipping it.
- Does alt text help SEO rankings directly?
- It's a supporting signal for Google Images and for reinforcing a page's topical relevance, not a primary ranking factor for main-content search results. Its biggest direct value is accessibility, with SEO benefit as a secondary effect.
- How long should alt text be?
- Keep it concise and specific — roughly under 125 characters is a safe practical limit, since some screen readers truncate longer strings. Describe what's shown and its function without padding it with unrelated keywords.
- Can alt text hurt SEO if done wrong?
- Yes — keyword-stuffed alt text unrelated to the actual image is a recognisable spam pattern that search engines discount, and at scale it can contribute to a broader impression of manipulative on-page optimisation across the site.
A hero image on a plumbing service page: alt="Licensed plumber repairing a burst pipe under a kitchen sink in Austin, TX" — specific, accurate, and naturally includes genuine context rather than stuffed keywords.
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