A theme describes the world. A core loop describes what a player repeatedly does inside it. Before drawing a large map or planning a shop, write the action, feedback, outcome and restart in four short lines.
Give the player one verb
Consider a parcel-delivery prototype. The player picks up one parcel, follows a visible route and drops it at one destination. There is no inventory expansion, vehicle shop or daily reward yet. Those features may become useful later; none is needed to find out whether the basic delivery is understandable.
Make the result observable
Write a question that a session can answer: can a new player deliver the parcel without verbal help? Record what they do, where they stop and which cue they notice. “It feels confusing” is a starting point. “The player walks past the destination three times because its marker resembles the pickup marker” gives you something concrete to change.
Keep a boundary beside the idea
List three things excluded from this build. For the parcel example, that could be multiple destinations, saved progression and a timer. This is a temporary scope decision, not a statement about the finished game. If a requested feature does not help answer the current question, put it on a later list.
Choose the next experiment
After the test, change one important uncertainty. You might adjust the destination marker and repeat the same task with someone new. Keep the old build label and the new observation together. A small prototype becomes valuable when it supports a clear decision, even when that decision is to simplify the idea.
Further reading
These are original learning notes. Check the current official documentation when implementing platform features.