Product Description SEO: How to Write Product Content That Meets Google and Merchant Center Requirements

Product description SEO is really two different jobs that are easy to confuse. One is writing content that convinces a customer to buy — something Google doesn't regulate directly, beyond the general rule that content should be made for people, not for an algorithm. The other is meeting the concrete, countable requirements of Google Merchant Center — character limits on the title and description, a minimum image size, a GTIN — which decide whether and how a product shows up in free shopping results or in ads. This article treats the two layers separately, because mixing them up leads to two common mistakes: copying the manufacturer's description and hoping "Google will understand," or writing a long, persuasive description that doesn't meet a single one of Merchant Center's formal requirements.

What Google expects from product content

Search Central doesn't have a dedicated "how to write a product description" page — we didn't find one, despite checking the whole e-commerce section. There are, however, two sources that together give a clear frame.

The first is the general principle of people-first content. Google's automated ranking systems "are designed to prioritize helpful, reliable information that's created to benefit people, and not content that's created to manipulate search engine rankings." On E-E-A-T (experience, expertise, authoritativeness, trustworthiness), Google sums it up this way: "Of these aspects, trust is most important. The others contribute to trust, but content doesn't necessarily have to demonstrate all of them." Google also offers self-assessment questions, including: "Are you using extensive automation to produce content on many topics?" and "Are you mainly summarizing what others have to say without adding much value?" — a question that applies directly to a copied manufacturer description.

The second source is Search Central's dedicated page on writing high-quality reviews — written with reviews in mind, but its logic, in our view, carries over well to any product content meant to convince a customer. Google's advice: "Evaluate from a user's perspective," "Demonstrate that you are knowledgeable about what you are reviewing — show you are an expert," and "Explain what sets something apart from its competitors." On length, Google is direct: "When writing reviews, focus on the quality and originality of your reviews, not the length, following as many of the above best practices as you are able." That line directly contradicts the popular advice that "a description needs 300–800 words" — Google doesn't publish any specific word-count limit; what matters is whether the description actually says something an identical competitor's description doesn't.

Product title and description — Merchant Center limits

No matter how well a description is written for the customer, if you want the product to appear in Google's free shopping results or in ads, you need to fit the formal limits of Merchant Center's product data specification:

• Title `[title]` — maximum 150 characters. Google's advice: describe the product accurately, matching the title on the landing page; "don't include promotional text like 'free shipping', all capital letters, or gimmicky foreign characters"; for variants, include the distinguishing feature (size, colour).
• Description `[description]` — maximum 5,000 characters. It should match the landing page description, avoid promotional phrasing and all caps, and "include only information about the product" — no links to your store, no sales information, no details about competitors, other products or accessories. Basic formatting (line breaks, lists, italics) is respected.

Google marks both attributes as "Required for each product," and missing product information can get a product disapproved — without a title and description in the feed, the product won't appear in ads or free listings, no matter how good the copy on the product page itself is. That's a distinction worth keeping straight: the content on the product page and the data submitted to Merchant Center are formally two separate datasets that should agree, but aren't the same file.

Product images — new requirement from 31 January 2027

Merchant Center's product data specification also carries an image requirement that isn't enforced yet, but has a fixed start date. Google writes: "We recently announced new image size requirements of at least 500 x 500 pixels for all product images. Enforcement of the new requirements will begin January 31, 2027." In other words — as of today (1 October 2026), the requirement is announced but not yet active. If you're planning a product photo shoot or a catalogue migration, this is a good moment to set your minimum resolution above 500×500 px ahead of time, rather than fixing the catalogue under deadline pressure once 2027 arrives.

Accepted formats are JPEG (.jpg/.jpeg), WebP (.webp), PNG (.png), non-animated GIF (.gif), BMP (.bmp) and TIFF (.tif/.tiff). The image itself can't "include promotional text, watermarks, or borders" — if your layout needs those elements, they belong on the page, not burned into the file submitted to Merchant Center.

Category descriptions — when they help, and when they hurt

Category page SEO is a frequent question, because intuition says a category page with no text at all is wasted SEO potential, while a page with a long block of text above the product grid clutters the interface. The truth is closer to a mechanism than a magic word count: a category description helps when it gives Google and the customer context the product grid alone doesn't provide — how the subcategories differ, what people typically ask when choosing, what the filters actually mean — and hurts when it's thin, generic copy lifted from an "about us" template and repeated across two hundred category pages with no real difference between them.

It's also worth correcting a myth that keeps circulating: "Google penalizes duplicate content." Current Search Central documentation says otherwise. On pages with no canonical URL set, Google writes: "If you don't specify a canonical URL, Google will identify which version of the URL is objectively the best version to show to users in Search" — and the reasons to still set one are control over which URL is shown, consolidating ranking signals, and preserving crawl efficiency, not avoiding a penalty. That's a change in wording, not in mechanism: the classic Search Central blog post from September 2008 said the same thing more bluntly — "There's no such thing as a 'duplicate content penalty.'" — quoting the help article in force at the time: "Duplicate content on a site is not grounds for action on that site unless it appears that the intent of the duplicate content is to be deceptive and manipulate search engine results." That sentence no longer exists as current documentation — it's historical context from 2008 only — but the mechanism it described hasn't changed in today's milder version: Google picks a canonical version to show, it doesn't penalize a whole site for duplicates simply existing.

The practical takeaway for category descriptions: a duplicated, empty category description won't bring any "penalty" down on the shop — but it won't help either, because it gives Google no new signal about how that page differs from the others. If you write a category description, write it to answer a question the product list itself doesn't answer — otherwise, better not to write one at all than repeat the same paragraph two hundred times.

Manufacturer descriptions and AI-generated content

Copying the manufacturer's description is an easy way to end up with content identical to every competitor's — and, as above, that isn't automatically "penalized," but it doesn't make the product stand out either, since Google still has to pick which of the identical versions to show.

Mass-producing content — including AI-generated content — falls under a separate, named policy. On 5 March 2024, Google announced three new spam policies, including scaled content abuse: "Scaled content abuse is when many pages are generated for the primary purpose of manipulating search rankings and not helping users," with one listed method being "using generative AI tools or other similar tools to generate many pages without adding value for users." Google notes that violating its spam policies means a site "may rank lower in results or not appear in results at all."

This isn't a ban on using AI for product descriptions — Google's separate generative-AI guidance is notably more permissive: "Generative AI can be particularly useful when researching a topic, and to add structure to original content." The line is scale without value: mass-generating hundreds of descriptions with no review, adding nothing the manufacturer's own copy didn't already say, "may violate Google's spam policy on scaled content abuse." A practical frame: AI as a tool to speed up writing and structuring a description that still passes through someone who actually knows the product — not as a generator of thousands of unsupervised pages.

If a product page also carries reviews or ratings marked up with review/aggregateRating structured data, one more rule applies. Google's review snippet guidelines say: "Don't include fake or undisclosed incentivized reviews on your page or in your structured data markup." The examples Google gives are reviews "that aren't based on a genuine experience of a product or service" and reviews "written in exchange for a benefit (such as money, discounts, vouchers, or free products) that don't clearly and prominently disclose the incentivization." So an incentivised review isn't banned outright — an undisclosed one is.

GTIN and attributes — when the number is required, and when it isn't

A GTIN (Global Trade Item Number — in practice a UPC, EAN, JAN or ISBN) is a separate product-data attribute, not part of the description text, but it affects a product's visibility. Google writes: "The GTIN [gtin] attribute is strongly recommended if the product is widely manufactured and has a GTIN," and on what happens without it: "Products with an assigned GTIN, but submitted without one, may have limited visibility."

A GTIN isn't universally required, though: "Not all products have unique product identifiers. However, if your product does have one providing it can help make your ads and listings richer." Google lists examples of products that may not have an assigned GTIN : store brand products, replacement parts, original equipment manufacturer (OEM) parts or replacements for them, custom-made products (custom T-shirts, art, handmade goods), books released before ISBN became an ISO standard in 1970, vintage or antique products, and pre-order products. For these, Google asks for brand and MPN instead of a GTIN.

One thing here is flatly prohibited: "Don't make up, guess, or include values from similar products." Typing in a random EAN just to "fill the field" runs directly against this rule — if a product genuinely has no GTIN, the right path is brand and MPN.

Product description SEO checklist

The two layers above — content written for the customer, and the formal data Merchant Center requires — involve different fields, and fail in different ways. Broken content (a copied description, no context, zero difference from competitors) doesn't block anything technically — the product still displays, it just won't convince the customer or stand out to Google among identical versions sold elsewhere. Gaps in the formal data behave differently: without a title and description, a product can't appear in ads or free listings at all; a product with an assigned GTIN submitted without it may have limited visibility; and from 31 January 2027 Google will start enforcing a minimum image size of 500×500 px, regardless of how well the on-page copy reads. That's why the checklist below mixes both layers in order: customer-facing content first, then the data submitted to Merchant Center, then the items that concern the whole catalogue rather than a single product.

Bringing the above into one list to run through for every new product, or when auditing an existing catalogue:

• The product title on the page matches the title submitted to Merchant Center and stays within 150 characters in the product data.
• The description's opening line says something the manufacturer's copy doesn't — a specific benefit or usage context, not a copied spec paragraph.
• The description stays within 5,000 characters in the Merchant Center data and contains no links to your store and no competitor mentions.
• The main image is at least 500×500 pixels (aim higher, ahead of enforcement starting 31 January 2027), with no promotional text or watermark burned into the file.
• Technical specifications sit separately from the benefits copy — a table or list, not mixed into the marketing text.
• The GTIN is submitted if the product has one; if it doesn't, brand and MPN are submitted instead — no number is guessed.
• The category description, where one exists, answers a question specific to that category rather than repeating the same paragraph on every category page in the shop.
• Reviews and ratings marked up with structured data come from genuine experience of the product, and any review written in exchange for a benefit says so clearly and prominently.
• Content isn't mass-generated without review — if you use AI, the final description still passes through someone who knew the product before it was written.

If you'd rather run this checklist with someone who does it for your whole catalogue and flags which products lose the most from Merchant Center mismatches, get in touch — product descriptions are also a topic that regularly comes up during an ecommerce SEO ranking review.

Sources

Google Search Central — Creating helpful, reliable, people-first content

Google Search Central — Writing high-quality reviews

Google Merchant Center Help — Product data specification: title, description and image requirements

Google Merchant Center Help — GTIN and other unique product identifiers

Google Merchant Center Help — Title attribute

Google Merchant Center Help — Description attribute

Google Search Central — Review snippet structured data

Google Search Central — Consolidating duplicate URLs

Google Search Central Blog — Demystifying the "duplicate content penalty" (2008)

Google Search Central Blog — New spam policies ahead of the March 2024 core update

Google Search Central — Spam policies for Google web search

Google Search Central — AI-generated content