A prototype is not a deliverable. It is a question made tangible — a way of testing whether a design decision holds up before the cost of building it becomes real.
The question is not whether to prototype. It is what to prototype, at what fidelity, for what purpose, and at what point in delivery. Getting those decisions right determines whether prototyping accelerates the work or adds to it.
What this topic covers
Prototyping guidance tends to focus on tools — which application to use, how to create animations, how to share a file for review. That is useful but it is not the hard part.
The hard part is the thinking that happens before the tool is opened: what question does this prototype need to answer, what is the minimum fidelity required to answer it reliably, and how will the findings from testing it feed back into the design.
This topic covers that thinking. It is guidance for practitioners who already know how to use prototyping tools and want to use them more deliberately — producing prototypes that answer real questions at every stage of delivery, not just ones that look finished.
Core areas of practice
Fidelity decisions
The fidelity of a prototype should be determined by the question it is trying to answer, not by how much time is available or how polished the output needs to look. Low-fidelity prototypes answer structural and conceptual questions. High-fidelity prototypes answer interaction and detail questions. Using the wrong fidelity for the question wastes time and can produce misleading findings.
Prototype planning
A prototype without a clear testing objective is just a design in a different format. Planning covers how to define the question a prototype needs to answer, how to scope it to the minimum necessary to answer that question reliably, and how to structure a testing session around it.
Testing approaches
Different testing objectives require different testing approaches. Concept testing, task-based usability testing, and unmoderated remote testing each produce different kinds of evidence. Understanding which approach fits which question — and what each one cannot tell you — is as important as the prototype itself.
Coded prototypes
For services that need to test interaction behaviour, performance under real conditions, or accessibility in practice, coded prototypes offer capabilities that design tool prototypes cannot match. This area covers when a coded prototype is the right choice, how to scope one appropriately, and how to use tools like the GOV.UK Prototype Kit effectively in a delivery context.
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