Claude Skill: SEO And AIO-optimized Alt Text Generator for Substack

How AI Overviews Changed What Your Image Descriptions Need to Do. And a Claude Skill That Writes Them for You

Jan 01, 2026

∙ Paid

Google used to treat alt text like a metadata field. A label for crawlers. We’d type “productivity-chart.png,” maybe throw a keyword in, and move on.

That’s not how it works anymore.

AI Overviews and multimodal search engines like Gemini don’t just read our alt text, they parse it as a semantic unit. They extract meaning, map entities, and decide whether your image deserves to show up as a standalone answer snippet.

Which means our alt text isn’t a label anymore. It’s a micro-piece of content.

So we need to stop writing it like it’s 2019.

Minimal three-dot horizontal divider on a black background, used as a section separator in Product With Attitude by Karo Zieminski, signaling a pause, transition, and reflective break in long-form writing.

What Changed

Traditional Google Image Search matched keywords. You wrote “Substack growth chart,” Google matched it to a query, done.

AI-powered search does something different. It reads your alt text alongside the image, the surrounding copy, and the page structure -- then decides what the image means. An AI recognizes “Substack subscriber growth chart showing 340% increase after viral post” as a specific, meaningful entity. Not just a nice phrase.

Here’s the practical consequence: AI Overviews frequently surface images with their alt text as standalone answer snippets. If your alt text can’t stand on its own and still deliver value, you’re invisible in the new search landscape.

The Principles That Matter

After digging through Google’s documentation, accessibility guidelines, and the emerging AIO optimization research, five principles hold up:

Accessibility first, SEO second. Start by describing what a visually impaired reader would miss. That description is your alt text spine, you optimize from there, not the other way around.
Entity-rich, not keyword-stuffed. Name specific tools, brands, concepts, and actions. One clean, natural keyword beats three awkwardly jammed in. Always.
Context over appearance. A chart showing “revenue growth” matters more than “a bar chart with blue bars.” Describe the image’s purpose, not its surface-level visuals.
125-200 characters. Google indexes roughly 16 words as a ranking signal. Screen readers chunk at 125 characters. This range serves both without getting cut off.
Write for AI parsability. Treat each alt text as a self-contained unit of meaning that an AI system can lift out and reuse as a standalone snippet.

I Built a Skill for This

I got tired of manually applying these rules every time I dropped an image into a Substack post. So I built a Claude Skill that does it automatically.

Here’s what it does: when you attach any image, it analyzes the visual content and outputs two things:

An alt text (125-200 chars, entity-rich, naturally keyworded, accessibility-compliant)
An SEO filename (3-7 hyphenated words, .webp)

It infers the keyword from the image itself so you don’t have to specify one each time -- though you can override it.

The alt text is built for both traditional Google Image Search and the newer AI Overview / AI Mode citations. It’s written as a standalone semantic unit that Gemini and other multimodal models can extract and reuse. Not just a keyword string for crawlers.

Getting Started

Copy the skill code below and save it as SKILL.md in your Claude skills folder. Once it’s saved, attach any image and ask for alt text. The skill handles the rest.