Click-defence asset

The Engine Coverage Gap Test

Twelve checks that tell you whether you are measuring AI search visibility across every engine your buyers use, or measuring one engine and assuming the rest. Nothing you enter leaves this page.

0 / 12 checks passed
Tick the checks you can evidence today.
Why twelve checks and not one score. Ahrefs ran 15,000 long-tail queries through four assistants in early July 2025. On average only 12% of the URLs those assistants cited also ranked in Google's top 10, and the spread between engines was wide: Perplexity 28.6%, Gemini 8.6%, Copilot 8.2%, ChatGPT 8.0% in-text and 6.1% in its reference list. Against Bing the order inverts, with Copilot at 16.6% and Perplexity at 3.3%. A single measurement tells you about a single engine.

Layer 1: The prompt set

1. You have at least ten buyer-intent prompts, written as your buyer speaks

Not keywords. Full questions, in the phrasing a person types into an assistant.

Pass: 10 or more prompts on file.

2. None of the prompts contains your brand name

A prompt that names you measures recall of a name the engine was handed. The question that matters is whether you come up unprompted.

Pass: zero prompts mention your brand.

3. The set covers category, comparison and problem shapes

"Best X for Y", "A versus B", and "how do I fix Z" pull different sources. Testing only one shape measures only one slice of the funnel.

Pass: at least two prompts of each shape.

Layer 2: Engine coverage

4. You test on four engines or more

ChatGPT, Google AI Overviews, Perplexity and Gemini at minimum. The overlap data says results on one do not predict the others.

Pass: four or more engines in every run.

5. Copilot is either tested or explicitly ruled out

Copilot leans on Bing, where its overlap runs at 16.6% against 8.2% on Google. If your buyers sit in a Microsoft estate, leaving it out is a hole.

Pass: tested, or a written note saying why not.

6. You record the cited URLs, not only whether you were named

The URL tells you which page won and which of yours should have. A mention count tells you nothing you can act on.

Pass: URLs captured for every answer.

Layer 3: Measurement integrity

7. Your tool reports which engine each result came from

A blended "AI visibility score" hides the one thing the data says matters. Insist on the breakdown.

Pass: per-engine results, not a single index.

8. You run a positive control on every measurement run

Include a domain you know is cited for the query. If the control comes back "not cited", the run is broken and every zero in it is meaningless. This is the check almost nobody runs, and it is the one that caught our own tooling.

Pass: control returns "cited" before you read any other result.

9. You re-run the same prompts at least twice a quarter

Answers move. One run is an anecdote, and a single reading cannot tell a real change from normal variance.

Pass: two or more runs per quarter on an unchanged prompt set.

Layer 4: Action linkage

10. Every lost prompt is mapped to the page that should have won it

If no page on your site deserves to win a prompt, the gap is a content gap, not a visibility gap.

Pass: a named page for every lost prompt.

11. You know which competitor won each lost prompt, and on which URL

The winning URL is the specification. Read it before you write anything.

Pass: competitor and URL recorded for every loss.

12. Your fix list is content and authority work, not tool configuration

No tracker has ever made anyone citable. If the quarter's actions are all dashboard settings, nothing will move.

Pass: the majority of open actions change pages or earn third-party coverage.

How to read your score

Checks passedWhat it meansThe next move
0 to 4You are guessing. Any claim about AI visibility right now is an opinion.Build the prompt set first. Layer 1 costs an afternoon.
5 to 8You are measuring one engine and assuming the rest behave the same way. The overlap data says they do not.Add engines and the positive control before you spend another euro on content.
9 to 11Real coverage with a known gap. You can trust the direction of travel but not every number.Close the specific failing check. It is usually 8 or 11.
12A measurement programme rather than a dashboard subscription.Spend the time on the content and authority work the runs point to.