> ## Documentation Index
> Fetch the complete documentation index at: https://docs.siftly.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# What is Share of Shelf?
> Understand GEO for commerce: how AI shopping engines choose products, and the metrics Siftly Shopping uses to measure your presence on the AI shelf.
## The shift in shopping search
For years, winning ecommerce search meant ranking in a grid of results: optimize your product page, earn reviews, win the click. Shoppers scrolled, compared, and chose.
That model is changing fast. AI assistants like **ChatGPT Shopping**, **Google AI Mode**, **Google Shopping**, and **Perplexity** now answer shopping questions directly. Ask one for "the best electric toothbrush for sensitive gums" and it returns a short, curated **carousel** of product recommendations, each product a **tile** on a digital shelf.
There is no page two. A handful of products get recommended; everything else is invisible. **Share of Shelf** is the commerce equivalent of ranking: *of all the product tiles an AI assistant shows for prompts in your market, how many are yours?*
## SEO vs. GEO vs. GEO for commerce
| | Traditional ecommerce SEO | GEO (brand visibility) | GEO for commerce |
| ---------- | ------------------------- | ------------------------------- | ---------------------------------------- |
| **Target** | Search engine crawlers | AI language models | AI shopping assistants |
| **Goal** | Rank in the results grid | Get your brand cited in answers | Get your **products** on the shelf |
| **Unit** | A web page | A brand mention | A product tile |
| **Metric** | Keyword rank, clicks | Citations, share of voice | **Share of Shelf**, reliability, rank |
| **Levers** | Backlinks, on-page SEO | Authority, structured content | Product feeds, content, pricing, reviews |
GEO for commerce doesn't replace ecommerce SEO. It extends it. A strong product page still helps. But the signals that get a product onto an AI shelf are different enough to deserve their own strategy.
## How AI shopping engines pick products
AI shopping answers are assembled from three sources. Each is a lever you can pull.
### 1. Product feeds and structured data
Engines lean heavily on structured product data: your **Google Merchant Center** and **Google Manufacturer Center** feeds, and your **Shopify** catalog. Clean, complete, well-attributed products are far easier to recommend. See [Product Optimization](/shopping/content/product-optimization).
### 2. Retrieval from the web (citations)
Most AI shopping engines retrieve live content at answer time (reviews, buying guides, listicles, and retailer pages) and cite them. The sources they cite are the sources shaping the recommendation. See [Citations](/shopping/analytics/citations).
### 3. Model knowledge
Models carry baseline knowledge about well-established brands and products from training. A strong, consistent presence across the web raises your baseline likelihood of being recommended.
## The GEO-for-commerce playbook
Identify the prompts where competitors get recommended but you don't. These are your highest-leverage opportunities. Start on the [Visibility](/shopping/analytics/visibility) and [Conversations](/shopping/analytics/conversations) pages.
Make sure your feeds and catalog are complete and well-attributed. [Product Optimization](/shopping/content/product-optimization) rewrites titles, descriptions, and attributes for AI shopping and submits them to GMC and GMfC.
See which sources AI engines cite for your market and create content that deserves a place among them, including [blog Content](/shopping/content/blog) and [Collection Pages](/shopping/content/collections).
Watch your Share of Shelf move after each change. GEO for commerce is iterative. What works shifts as engines update and competitors adapt.
## Key metrics in Siftly Shopping
The share of visible product tiles that are yours, across a set of AI shopping responses. If AI assistants show 1,000 product tiles across your tracked prompts and 180 are yours, your Share of Shelf is 18%. It's your headline metric.
The percentage of tracked prompts where your brand appears at least once. Visibility measures **breadth**: how many of the shopping intents in your market you show up for at all.
The percentage of responses (runs) where your brand appears at least once. Reliability measures **consistency**: when the same prompt is asked repeatedly, how dependably do you show up?
The percentage of responses where your product appears in the first three tiles. Earlier tiles get far more shopper attention, so position matters as much as presence.
**RPI** compares your price to the competitive average for the same shelf. **Value Hit Ratio** is the percentage of your products priced at or below the competitor average, a quick read on how often you look like good value. Both live on [Commerce Control](/shopping/analytics/commerce-control).
Newly tracked products are in a **warm-up cohort** for their first 14 days and are excluded from your headline Share of Shelf, so adding products doesn't read as a sudden drop. Switch between the **mature** view (established products only) and the **full portfolio** view (including warming-up products) on the Visibility page.
GEO for commerce is an emerging field, and AI shopping platforms evolve rapidly. Siftly Shopping's analysis is continuously updated to reflect how the major engines retrieve, rank, and recommend products.