What is prompt coverage?
Prompt coverage is the share of the buyer questions in your category that your AI visibility checks actually test. Two prompts sample a sliver of the question space; meaningful coverage spans the whole buying journey, from unbranded research questions to direct comparisons.
Buyers in any category put far more than one question to an AI assistant. Someone choosing accounting software might ask for the best option for a small UK business, ask how two named products compare, ask whether a specific tool justifies its price, or ask for alternatives to the market leader. Prompt coverage measures how much of that question space your AI visibility testing spans. A brand measured against forty prompts across the buying journey has coverage. A brand measured against two has an anecdote.
Testing two prompts misleads because AI answers shift with phrasing. A brand can be recommended confidently when a buyer names it directly, then vanish from the unbranded category question where many buyers start. Accuracy varies between contexts too: in Discoverable's July 2026 study of 30 brands, 27 (90 percent) were misdescribed when the assistant answered from memory, and 13 (43 percent) still were when it used live web search. Two prompts cannot surface patterns like that. When both happen to go well they hand you false confidence, and either way they say nothing about the dozens of buyer questions that went untested.
Breadth has to come before trend. A weekly score built on two prompts moves with ordinary variation in the model's output, so the trend line is mostly noise. A score built on a broad, fixed prompt set is stable enough for movement to mean something. Discoverable's checks run via Claude with live web search, with other engines rolling out, and they test a spread of buyer questions rather than a single query. The paid plans re-run the same prompt set weekly, so the score trend is measured on a consistent base.
To judge your own coverage, write down every question a buyer could plausibly ask on the way to a decision in your category: unbranded questions where you want to be named, comparisons against each serious competitor, questions about specific use cases, and questions about pricing or fit. If your current monitoring tests only a couple of these, you are sampling rather than measuring. Discoverable's free checker requires no login and gives a starting read, and businesses with several distinct offerings can track separate prompt sets per product line on the Scale plan.