Every prototype claims to be interactive. The word does a lot of work, because it stretches from a PDF with clickable hotspots to software that runs. Before you build an interactive prototype, or trust findings from one, it helps to know which kind you are holding.
The four levels of interactive
Interactivity in prototyping is a spectrum, and most tools sit at one point on it.
- Linked screens. Static mockups wired together with hotspots: tap the button region and the next screen appears. This is the classic clickable prototype, and it is fast to make from screens you already have.
- Conditional logic in a design tool. Variables, toggled states, simple branching. The prototype can remember that you picked "annual billing" and show the matching price. Still no real data, but the facade is thicker.
- Coded prototypes. Real components, real state, throwaway everything else. These behave honestly under input but historically cost engineering time nobody wanted to spend on something disposable.
- Working software. The prototype runs the actual logic against actual data. At this level the distinction between prototype and product is a decision about scope, not a difference in kind.
Each step up costs more and answers more. The craft is matching the level to the question, a theme the prototyping pillar covers in depth.
What a facade can teach you
Clickable prototypes are underrated as thinking tools. Linking your screens forces you to define the flow, and watching someone else click through it exposes navigation problems in minutes. Facades are excellent at answering:
- Can people find the thing? Do they understand what each screen is for?
- Does the order of steps match how people think about the task?
- Which labels confuse, and where do people expect to go back?
They are also cheap. When the question is purely structural, a facade built in an afternoon is exactly the right amount of prototype, the same way a grey-box wireframe is the right amount of design early on. If the vocabulary around these artifacts is fuzzy on your team, the wireframe vs mockup vs prototype guide draws the lines.
Where the facade lies
The trouble starts when a clickable prototype is asked questions it cannot answer. Facades lie about four things, all of them consequential:
- Data. The screens show one happy, hand-picked record. Real content is longer, emptier, or weirder, and layouts that looked fine collapse.
- Input. Testers tap through fields they never type in. Whether the form is actually pleasant to fill remains unknown.
- Latency and states. Everything responds instantly and nothing loads, errors, or sits empty. Users never meet the states they will live in.
- Edge cases. The facade has one path. The product has hundreds.
Usability findings built on those lies can evaporate against the real thing. A checkout that tested clean as a facade can still fail in production testing, because the friction was in the typing, the validation, and the wait, none of which the facade contained.
The cost gap collapsed
The reason teams settled for facades was never preference. Coded prototypes answered better questions, but the cost gap between wiring hotspots and writing working screens was enormous, so level one won by default.
Agents closed that gap. Describing a screen to an AI agent that writes real code now takes about as long as linking mockups used to, and the result is a functional prototype: it accepts input, holds state, and breaks honestly. On an agent canvas, asking for a working prototype instead of a clickable one is no longer a schedule decision. When the working version costs the same, the default level of "interactive" rises to "it actually runs." That shift is also what makes rapid prototyping rapid in practice rather than just in name.
Testing with an interactive prototype
Whatever level you test at, a few habits keep the findings honest:
- Use realistic data. Long names, empty lists, ugly numbers. If the prototype only shows the demo record, you are testing the demo.
- Let people type. Real input is where forms fail. A prototype that cannot accept it is silent on the question.
- Watch for the edge of the facade. Note every moment a tester tries something the prototype cannot do. That list is your map of what the next level of fidelity must include.
- Retest across levels. Structural findings from the facade, input and data findings from the working version. One round of each beats three rounds of either.
The facade still has a place. It is the sketch of interaction, quick and disposable, and sketches are valuable. Just know which questions it is answering, and move to a prototype that runs before you bet on the answers.