Are alt texts really as flexible as Google claims?

What does Google really mean by "flexibility" of alt texts?

The phrasing of John Mueller plays on ambiguity. Flexibility does not mean you can write anything, but that you must adapt the description to the real context of the image on your page.

Specifically: if your image shows an orange cat on a gray sofa, your alt must describe exactly that—not "best modern design sofa" because you sell sofas. Google now detects glaring inconsistencies between visual content (analyzed by its vision algorithms) and the alt text.

Why does accessibility come before SEO?

Screen readers remain the primary reason for the existence of alt texts. A visually impaired person navigating with NVDA or JAWS must instantly understand what the image represents.

Google relies on this accessibility principle to assess the quality of alt texts. An alt stuffed with keywords but unintelligible to a human will be considered spam—even if technically, it remains indexable. The logic: if it’s not useful for a user with a disability, it’s not relevant for indexing.

How does Google distinguish a relevant alt from an over-optimized alt?

Google's computer vision algorithms analyze the actual visual content: objects, embedded text, context, composition. They then compare this analysis with your alt attribute and the surrounding text.

A significant discrepancy triggers signals of algorithmic manipulation. A typical example: an image of a white product on a white background with an alt of "cheap women’s running shoes sale" while the visual analysis simply detects a sneaker. Google knows you’re forcing it.

• Factual description: describe what is visible, not what you’d like to rank for
• Page context: the alt must logically fit within the adjacent textual content
• Reasonable length: 10-15 words maximum, not 30-word sentences packed with variants
• Visual consistency: what Google "sees" via its algorithms must match your description
• Uniqueness: avoid identical alts on different, even similar, images

Is this guideline consistent with what is observed in the field?

Yes and no. On Google Images, sites that apply simple descriptive alts actually perform better than those that engage in blatant keyword stuffing. We regularly verify this through e-commerce audits.

However, the notion of "flexibility" remains vague. [To be verified]: Google has never published a precise threshold defining when an alt becomes "over-optimized." Penalties (or rather demotions) appear to be applied on a case-by-case basis, leaving frustrating room for interpretation for practitioners.

What nuances should be applied to this recommendation?

First point: the recommendation applies differently depending on the type of site. A media outlet showcasing news does not have the same constraints as an e-commerce site with 50,000 product listings. In the latter case, the "factual" description of a product may legitimately include commercial attributes (color, material, use) that look similar to keywords.

Second nuance: Google does not say to completely avoid keywords, it says to avoid irrelevant keywords. A crucial subtlety. If your image indeed shows "women's running shoes," using it in the alt is perfectly legitimate. The problem arises when you add "cheap" while there are no visible price indicators on the image.

In what cases does this rule not apply strictly?

Pure decorative images (separators, generic icons, backgrounds) can have an empty alt (alt="") without negative impact. This is actually recommended to avoid polluting the experience of screen readers.

Complex graphics and infographics pose a real challenge: a 12-word alt is not enough to describe a data chart. In this case, best practice is to combine a short alt summarizing the essentials + a longer description via the longdesc attribute or visible adjacent text. Google takes this expanded context into account.

What should you concretely do with your existing images?

Start with an audit of your current alt texts. Extract them via Screaming Frog or Sitebulb, then identify problematic patterns: mass identical alts, excessive lengths (>20 words), presence of repetitive keywords not justified by the visual content.

Then, prioritize rewriting based on potential impact: pages generating Google Images traffic first, then strategic pages (product sheets, landing pages), and finally editorial content. Do not attempt to redo everything at once on a large site—you will lose qualitative consistency.

What mistakes should be absolutely avoided in your new alt texts?

Classic mistake #1: using the filename as alt by default. "IMG_3847.jpg" or "product-ref-12345.jpg" adds nothing. Even a CMS that auto-generates alts from filenames should be configured to clean and humanize these strings.

Mistake #2: repeating the H1 title of the page as alt on the main image. It’s redundant, and Google detects it as internal duplicate content. The alt should provide complementary information, not paraphrase what’s already written right next to it.

How can you check that your alts respect best practices?

Test your pages with a real screen reader (NVDA is free on Windows). Navigate without seeing the screen: are your alts understandable? Do they allow comprehension of the content without ambiguity? If you hesitate or it sounds odd, the alt is probably over-optimized or poorly written.

On the technical side, ensure that your <img> tags systematically include an alt attribute (even if empty for decorative images). A missing alt is an accessibility error reported by Lighthouse and can weigh in Google’s overall quality assessment. For sites with a large volume of images, these optimizations often require a partial overhaul of editorial and technical workflows—calling on a specialized SEO agency may prove wise to structure this migration without breaking existing setups.

• Extract all alt texts via an SEO crawler and identify duplicates
• Rewrite alts by factually describing what the image shows
• Limit the length to a maximum of 10-15 words per alt
• Check the coherence between alt and surrounding textual content
• Test with a screen reader to validate understanding
• Integrate alt writing into the editorial workflow (writer briefs, CMS templates)