Alt Text Character Limit: How Long Should Image Alt Text Be?

Alt text — the alt attribute on an HTML <img> tag — describes an image for anyone who can't see it: a screen reader user navigating a page, a browser that failed to load the image, or a search engine trying to understand what the image depicts. Unlike meta titles and descriptions, alt text doesn't have a single well-known official limit, which leaves most writers guessing — usually erring toward either too short to be useful or too long to be read comfortably.

Why Alt Text Serves Two Different Purposes

Accessibility. Screen reader software reads the alt text aloud in place of the image, exactly as written, to users who are blind or have low vision. This is the original and primary purpose of the attribute, and it predates any SEO consideration by years — alt text is an accessibility requirement (part of the Web Content Accessibility Guidelines) independent of any search engine benefit.

Search engine understanding. Google cannot see an image the way a human can; alt text is one of its primary signals for understanding what an image depicts, which affects both regular search rankings and specifically Google Images results. A well-written alt text can help an image rank in image search and can reinforce the topical relevance of the surrounding content.

These two purposes mostly align — a clear, accurate description serves both — but they pull in slightly different directions when it comes to length, which is where the practical guidance gets useful.

The Practical Character Limit

Context	Recommended length
General guidance	Under 125 characters
Screen reader practical limit	~125 characters (some older readers truncate beyond this)
Google's technical limit	No official cap, but very long alt text may be partially ignored
Decorative images	Empty alt text (alt="") — zero characters, deliberately

The 125-character figure comes from older screen reader software, which historically truncated alt text beyond that length. Modern screen readers generally handle longer text without cutting it off, but 125 characters remains a reasonable practical target because it forces concision — a genuinely useful description of most images doesn't need much more than that to communicate what matters.

The character limit for alt text is less about a hard technical wall and more about a discipline: if a description needs 300 characters, it's very likely describing more than the image actually shows, or describing it with more detail than a listener needs in the middle of reading a page.

What Makes Alt Text Good, Independent of Length

Describe what's actually relevant to the content, not everything visible. An image of a person at a desk, used to illustrate an article about remote work, doesn't need alt text describing their clothing, the color of the desk, or the artwork on the wall behind them — none of that is relevant to why the image is on the page. "A person working at a desk with a laptop and notebook" conveys what matters.

Don't start with "image of" or "picture of." Screen readers already announce that the element is an image before reading the alt text, so prefacing the description with "image of" or "photo of" is redundant — it uses up character budget without adding information the listener doesn't already have.

Include specific, meaningful text that appears in the image, when relevant. If an image contains an infographic, a quote, or a chart with a specific data point that matters to the content, that specific information belongs in the alt text (or, for complex charts, in the surrounding page content with the alt text pointing to it) rather than a generic description that misses the actual informational content.

Skip alt text entirely for purely decorative images. An image used only for visual styling — a background texture, a decorative divider — should have an empty alt="" attribute, which tells screen readers to skip it entirely rather than announcing a description of an image that carries no informational content. This is different from omitting the attribute altogether, which some screen readers handle by reading the file name instead — often a meaningless string like "IMG_4521.jpg."

Alt Text vs Image File Name vs Image Title

These three are sometimes confused. The alt text is what's announced by screen readers and evaluated by search engines for image understanding. The file name (ideally descriptive — "home-office-desk-laptop.jpg" rather than "IMG_4521.jpg") provides a secondary, weaker signal to search engines about image content. The title attribute (a separate, optional HTML attribute) shows as a tooltip on hover in most browsers and is not read by most screen readers by default — it serves neither purpose as reliably as alt text does, and is generally less important to get right.

Where Alt Text Fits Into the Broader Character-Limit Picture

Alt text is one of several page elements with a practical, though not always officially fixed, length guideline — alongside the meta title, meta description, and H1, covered together in our post on checking every SEO character limit before you publish. Unlike the meta title and description, which are truncated by a hard pixel-based display limit, alt text's limit is softer and driven more by usability and accessibility best practice than by a strict technical cutoff — but the discipline of checking length before publishing applies equally well to all of them.

Pasting a batch of alt text descriptions into a character counter before publishing — particularly for content with many images, like a product catalog or a photo-heavy article — catches descriptions that have drifted too long or stayed too vague, in the same few minutes it takes to check meta titles and descriptions for the same content.

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Alt text doesn't have the same hard, pixel-measured limit that meta titles and descriptions do, but the practical target — concise, specific, under roughly 125 characters — serves both of its actual audiences well. A screen reader user gets a quick, useful description instead of a paragraph; a search engine gets a clear signal about what the image shows instead of a vague or padded one. Getting the length right is less about a rule and more about respecting what both audiences actually need from a few seconds of description.