Writing good image alt text for a single new image is straightforward once you know the rules. The harder problem is everything that’s already published — hundreds or thousands of images, accumulated over years, across however many people have touched your CMS. This is the practical process for finding what’s broken and fixing it without manually opening every page.
If you haven’t yet, it’s worth a quick read of our overview on why alt tags matter for SEO first — this post assumes you already know why you’re doing this and just need the how.
Step 1: Do a quick manual check first
Before reaching for a full crawl, it helps to spot-check a few pages by hand so you know what you’re dealing with. Right-click any image in your browser and inspect the element — you’ll see immediately whether the alt attribute is present, empty, or missing entirely. Doing this on five or six representative pages (homepage, a product page, a blog post) gives you a fast read on how widespread the problem is before you commit to a full audit. Search Engine Land’s quick accessibility check walkthrough covers this exact process if you want a step-by-step.
Step 2: Run a full site crawl
For anything beyond a handful of pages, manual checking doesn’t scale. SEO crawling tools can flag every image with missing, empty, or duplicated alt attributes across your entire site in one pass:
- Search Console will surface some image indexing issues, though it’s not built specifically for alt text auditing
- Site audit tools (Semrush, Screaming Frog, Ahrefs) can crawl every page and generate a report of images missing alt attributes, alt text over the recommended length, or identical alt text repeated across multiple images
- Browser accessibility tools like Lighthouse (built into Chrome DevTools) or WAVE will flag missing alt text alongside other accessibility issues on a per-page basis
Semrush’s image SEO guide walks through running this kind of audit with their Site Audit tool specifically, including how to filter results down to just the alt attribute issues.
Step 3: Prioritize before you fix anything
A full crawl on a large site can return thousands of flagged images, and trying to fix all of them at once is how audits stall out. Triage instead:
- High-traffic pages first — your homepage, top landing pages, and best-performing blog posts get priority over a forgotten page from three years ago
- Product and category pages next — these are where missing alt text most directly costs you image search traffic
- Everything else can wait — a low-traffic archive page with a missing alt attribute isn’t where your time is best spent
Step 4: Know what you’re likely to find
Once the crawl results are in, the issues tend to cluster into a predictable set of patterns — missing alt text, near-identical descriptions repeated across product variants, and alt text left over from a swapped image that no longer matches what’s shown. We’ve covered each of these in more depth, with what to do about them, in 7 alt text mistakes that are quietly hurting your SEO — worth a read alongside your audit results so you’re fixing the right thing rather than just filling in the blank field.
Step 5: Fix at scale, not one image at a time
For a few dozen images, fixing them by hand is fine. For a few thousand, you need a different approach:
- CMS bulk-editing tools — most modern CMS platforms (WordPress, Shopify) support bulk image metadata editing through plugins or built-in tools, rather than opening each image individually
- AI-assisted generation — increasingly common for large catalogs, where writing thousands of individual descriptions by hand simply isn’t practical. These tools can generate a solid first draft from the image itself, but they still need human review — an AI description that’s technically accurate but contextually generic defeats the purpose just as much as no alt text at all
- Standardize a naming and writing convention going forward, so whoever’s uploading images next — whether that’s a person or a workflow — has a consistent pattern to follow rather than reinventing the approach each time
Step 6: Build it into your ongoing process, not just a one-time cleanup
An audit fixes what’s broken today. Without a process change, the same gaps reappear within months — new images get added without alt text, existing images get swapped without anyone updating the description. The fix is procedural: add an alt text field as a required step in your image upload or content-publishing checklist, so it’s not something that gets caught after the fact.
The takeaway
Auditing alt text isn’t glamorous work, but it’s one of the few SEO tasks with a genuinely finite scope — you can actually finish it, measure the before-and-after, and move on. Start with a quick manual spot check to gauge the scale of the problem, run a full crawl once you know what you’re looking for, prioritize by traffic, and build a habit so you’re not doing this same audit again next year.
This post is part of a series on image SEO. Start with the overview: Are Alt Tags Important for SEO? Or continue to: How to Write Alt Text That Works · 7 Alt Text Mistakes Hurting Your SEO · Alt Text vs. Title vs. Caption