Pick a question, not a feature list
Choose a question you can answer through play: is it satisfying to redirect a rolling object, or does sorting feel better when the container space is limited? Build the smallest loop that exposes that question. A hobby prototype is useful even if it lasts one level, provided you can observe a result and revise the rule.
Use a bounded prototype recipe
Example prompt: “Create a one-screen sorting puzzle with four colored pieces and two containers. Drag one piece at a time; the goal is to place all pieces into the matching container. A wrong placement returns the piece and briefly highlights the mismatch. There is no timer. Restart clears both containers and restores the same starting order. Keep the pieces large enough to drag and display the matching colors on both pieces and bins.” After one build, record what you expected each drag to do and whether it did so.
Spend the next hour on evidence
Test the easiest correct move, an incorrect move, and a full solution. If a tester hesitates because two colors are hard to tell apart, change the labels before changing the puzzle. If every move is obvious, add one constraint such as a limited container capacity, then see whether it creates planning rather than busywork.
Save the idea and the one question it is meant to answer. A hobby project can stop after a useful experiment; you do not need to turn every prototype into a long-running game with progression systems.
Questions about game ideas for hobbyists
How do I keep a first hobby project small?
Limit it to one screen, one main action, one success condition, and a restart. Leave extra levels and upgrades out until the basic loop gives you a reason to keep building.
Is an unfinished prototype still useful?
Yes, if it answers a design question. Write down what happened during a few repeatable attempts, then decide whether to revise the rule, test another idea, or stop.