Why build a 15–30 minute vertical slice first?

A vertical slice is neither a trailer nor simply a shorter version of the whole project. It is playable content that meets a real quality target: character performances, choices, state changes, and consequences the player can perceive.

Four questions it should answer

Does the player understand their role?

Players need to understand their powers and constraints quickly. When establishing their identity requires lengthy narration, later choices often lack a clear basis.

Do choices carry a real cost?

An option need not lead immediately to another scene, but it must leave a perceptible change. Character attitudes, available information, and the terms of the next negotiation can all provide feedback.

Can states be tracked?

A prototype should include at least one state write and one later read. Otherwise, the team has tested a linear short film rather than an interactive system.

Is production sustainable?

Completing the same section exposes real filming problems. Must actors repeat an entire performance for a small variation? Is continuity difficult to maintain? Can post-production identify the state associated with each clip?

Choosing the slice’s scope

A useful slice usually contains a complete small objective, rather than mechanically taking the first twenty minutes of chapter one.

Include:

1. An immediate objective the player understands.
2. At least one important character who reacts proactively.
3. A choice made with incomplete information.
4. A consequence with a cost.
5. An unresolved question that makes the player want to continue.

What to observe after the prototype

Do not only ask whether it was fun. Record when players hesitate, why they interpret an option in a particular way, whether they notice state feedback, and which decision they want to revisit afterward.

If players can recount what they did but cannot explain what their actions changed, the problem is often the feedback chain rather than the wording.

A vertical slice does not exist to prove a plan correct. It uses the smallest complete experience to discover early where that plan fails.