---
title: "Variant pages an agent can read"
description: "An agent has to find the exact size and color, with its own price and stock. How to mark up product groups, feeds and variant URLs so it gets that right."
source_url: "https://specoria.com/insights/variant-pages-an-agent-can-read/"
lang: "en"
---

[Insights](https://specoria.com/insights/) Product data

# Variant pages an agent can read: sizes, colors and the product group

An agent has to find the exact size and color, with its own price and stock. How to mark up product groups, feeds and variant URLs so it gets that right.

By [Specoria Team](https://specoria.com/about/) October 24, 2026 8 min read

In this article

- [How an agent picks a variant](https://specoria.com/insights/variant-pages-an-agent-can-read/#how-an-agent-picks-a-variant)
- [The product group in structured data](https://specoria.com/insights/variant-pages-an-agent-can-read/#the-product-group-in-structured-data)
- [One URL per variant, or one page with a selector](https://specoria.com/insights/variant-pages-an-agent-can-read/#one-url-per-variant-or-one-page-with-a-selector)
- [The feed side: one group ID everywhere](https://specoria.com/insights/variant-pages-an-agent-can-read/#the-feed-side-one-group-id-everywhere)
- [Stock and price belong to the variant](https://specoria.com/insights/variant-pages-an-agent-can-read/#stock-and-price-belong-to-the-variant)
- [Common mistakes that hide a variant](https://specoria.com/insights/variant-pages-an-agent-can-read/#common-mistakes-that-hide-a-variant)
- [A practical checklist](https://specoria.com/insights/variant-pages-an-agent-can-read/#a-practical-checklist)
- [The bottom line](https://specoria.com/insights/variant-pages-an-agent-can-read/#the-bottom-line)

A shopper asks an assistant: "Find me this linen shirt in navy, size L, under €60." Finding the shirt is the easy part. The real work is finding that one combination, navy in L, and confirming that it is in stock and what it costs. If your store only says "several colors and sizes", the agent has to guess, click through options or move on.

In this article, we look at how agents pick a variant, how schema.org, Google and feeds describe a product group, and the mistakes that hide a variant. Our [catalog guide](https://specoria.com/insights/preparing-your-catalog-for-shopping-agents/) covered variants in one paragraph; this is the detailed version.

## How an agent picks a variant

An agent works with three layers: the product group (the shirt), the options it varies by (color, size) and the specific combination someone can actually buy (navy, L). Only the last one has a price, a stock status and something that can go into a cart.

Agent instructions make this explicit. The skill file Shopify publishes for agents using Shop MCP says that search shows one option combination, that "size filters and size lists do not prove that combination is in stock", and that before recommending or building a cart the agent should confirm that selection's stock and price. OpenAI's product feed spec says the same from the merchant side: one row per purchasable item or variant, each with its own price, availability, URL and images.

So the question is simple: can a machine read each combination as its own item, without clicking anything?

## The product group in structured data

Schema.org defines a `ProductGroup` as a group of products that vary only in well-described ways, such as size, color or material. The group itself is not offered for sale; its variants are. Google added support for this structure on February 20, 2024, with three properties:

- **`hasVariant`** nests each variant `Product` under its group. A variant can also point back to the group with `isVariantOf`.
- **`variesBy`** lists the properties the variants differ by. Google supports color, size, suggested age, suggested gender, material and pattern, referenced by their full schema.org URL (for example `https://schema.org/color`).
- **`productGroupID`** is the group's identifier, which Google also calls the parent SKU.

Google's guidelines add rules worth following even if search features are not your goal:

- Every variant needs a unique ID, such as `sku` or `gtin`. Every group needs a unique ID too.
- If you give the group ID both on the group (`productGroupID`) and on the variants (`inProductGroupWithID`), the two must match.
- Variant names should be more specific than the group name: "Wool winter coat, green, size small" rather than "Wool winter coat".
- Shared facts such as brand and material can sit once at group level, while each variant carries its own color, size, image and `Offer`.

## One URL per variant, or one page with a selector

**Single page.** All variants live on one page and change through a selector. Google asks for one canonical URL for the whole group, usually the page with no variant chosen. It also requires that each variant can be preselected directly with its own URL, typically through query parameters like `?color=green&size=small`. That page must show the variant's own image, price and availability and let the visitor add it to the cart.

**Multi page.** Each variant, or each color, has its own page. Google asks that each page carry full, self-contained markup, repeating the `ProductGroup` definition on every variant page.

Both can work. What does not work is a third pattern many stores have: a selector that changes price and stock on screen, with no address for a specific variant. An agent cannot link the shopper to "navy, L" or check it again later without repeating the clicks. OpenAI's feed spec asks for a product URL "with the variant selected when possible", and Google Merchant Center recommends a different landing page URL for each variant.

## The feed side: one group ID everywhere

In Google Merchant Center, the feed attribute for this is `item_group_id`. Each variant is submitted as a separate product with its own `id`, and all variants of the same product share one `item_group_id`. Google's own example: a T-shirt in 3 sizes and 3 colors is 9 separate products with the same group ID. The attribute is required for product variants in free listings.

Google's guidance for the group ID:

- Use the parent SKU as the group ID, and don't submit the parent SKU as a product of its own.
- Keep the value stable. If the group ID changes often, variants may be grouped inconsistently.
- Don't reuse a group ID for a different product, and don't rely on upper and lower case to tell two groups apart.
- Don't use a group ID for things that are similar but not variants, such as a suit sold as jacket and trousers.
- Make sure the landing page matches each variant's title, color, price, availability and image.

OpenAI's feed spec works the same way under different names: a shared `group_id` (it still accepts `item_group_id`), `listing_has_variations` set to true, and a `variant_dict` such as `{"color":"Black","size":"10"}`. It also states plainly that conflicting values are not reconciled for you.

The simplest rule: use one value, the parent SKU, in three places: `productGroupID` in structured data, `item_group_id` in Merchant Center and `group_id` in agent feeds. Google's documentation maps `item_group_id` to the schema.org group ID.

## Stock and price belong to the variant

A product group has no single price and no single stock status. Google's own example shows why: the small coats cost $39.99 and are in stock, while the large one costs $49.99 and is on backorder. One `availability` for the whole group hides which sizes are really there.

Give each variant its own `Offer` with `price`, `priceCurrency` and `availability`, matching the feed and the page. We explained why contradictions cost you in [your feed, your page and your structured data should agree on price](https://specoria.com/insights/feed-page-and-structured-data-should-agree-on-price/).

## Common mistakes that hide a variant

- **Markup that only exists after JavaScript runs.** Google recommends putting Product structured data in the initial HTML and warns that markup generated in the browser can make Shopping crawls less frequent and less reliable, which can be an issue for fast-changing data like price and availability.
- **Variant price only after a click.** If the real price appears only once a size is chosen, an agent has to try every option to compare. We listed this among the [33 details that tire a shopping agent](https://specoria.com/insights/what-tires-a-shopping-agent/).
- **Selectors that aren't real controls.** In our [field study with real browser agents](https://specoria.com/insights/ai-agents-shopping-in-a-real-browser/), stores that offered size and color as select boxes, radio buttons or plain buttons let agents finish in 3 to 6 steps. Offer options as real controls, not custom elements that only look clickable.
- **Colors that exist only as swatches.** A color shown as an image with no text name gives the agent nothing to match "navy" against. Name the option in text and in `color`.
- **One identifier for the whole family.** OpenAI's spec notes that a GTIN identifies a specific trade item, not the variant group. Each variant needs its own.

## A practical checklist

- Pick your 20 best-selling products that have variants.
- For each, open one variant's URL directly in a private window. Does the page arrive with that variant selected, showing its own price, image and stock?
- View the page source, not the rendered page. Is there a `ProductGroup` with `variesBy`, `productGroupID` and one `Product` per variant, each with its own `Offer`?
- Check that every variant has a unique `sku` or `gtin` and a specific name.
- Compare the group ID in your structured data, your Merchant Center feed and any agent feed. They should be the same parent SKU.
- Pick three variants, including one out of stock, and confirm that page, markup and feed agree on price and availability.
- Make sure size and color are offered as real form controls with text labels.

## The bottom line

Agents don't buy "the shirt". They buy navy in L at a price they can confirm. A store that describes each variant as its own item, under a stable parent ID, at its own URL, with its own price and stock, gives the agent a direct answer. A store that hides that behind a selector leaves the agent guessing.

Specoria checks how your product pages and variants read to an agent, from the structured data in the first HTML to whether a real browser agent can choose the right option and add it to the cart. Start with a [free readiness test](https://specoria.com/#contact).

### Sources

- Google Search Central, [Product variant structured data (ProductGroup, Product)](https://developers.google.com/search/docs/appearance/structured-data/product-variants), last updated September 8, 2026.
- Google Search Central Blog, [Adding structured data support for Product Variants](https://developers.google.com/search/blog/2024/02/product-variants), February 20, 2024.
- Schema.org, [ProductGroup](https://schema.org/ProductGroup), accessed October 20, 2026.
- Google Merchant Center Help, [Item group ID (item_group_id)](https://support.google.com/merchants/answer/6324507), accessed October 20, 2026.
- OpenAI, [Product Feed Spec](https://developers.openai.com/commerce/specs/feed), accessed October 20, 2026.
- Shop, [Shop MCP agent skill](https://mcp.shop.com/skill.md), accessed October 20, 2026.
- Specoria Insights, [We sent AI agents shopping in a real browser 40 times. Here's where they got stuck.](https://specoria.com/insights/ai-agents-shopping-in-a-real-browser/)

## Related

- [Your feed, your page and your structured data should agree on price: how shopping agents read a contradiction](https://specoria.com/insights/feed-page-and-structured-data-should-agree-on-price/)
- [How to prepare your product catalog for shopping agents](https://specoria.com/insights/preparing-your-catalog-for-shopping-agents/)
- [Guest checkout and AI agents: where a sign-in wall ends the purchase](https://specoria.com/insights/guest-checkout-and-ai-agents/)
- [Agent protocol map: UCP, ACP, AP2, MCP, WebMCP](https://specoria.com/agent-protocols/) What each protocol does and what the free test checks
- [Agentic commerce statistics](https://specoria.com/agentic-commerce-statistics/) Sourced, dated figures you can cite

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