Design for touch and small screens
For a game designer, this catalog design prototype should make every player action and result the player can inspect easy to evaluate. Write how to define item identity, value, Koin price, preview, and ownership before checkout. Choose the offer moment, explain the game benefit, and protect the complete free path. Compare the experience before and after ownership. Use comfortably separated confirm and cancel controls, readable Koin amounts, and a layout that survives portrait, landscape, browser chrome, and an on-screen keyboard without hiding the item.
Expect interruption
Simulate locking the phone, changing tabs, receiving a call, and returning with a slow connection. The player should see one understandable result and retain a safe route back to play.
State the platform limit
A mobile browser prototype is not an App Store or Google Play binary. Native billing APIs, device identity, refunds, entitlements, and submission need separate implementation and review.
Judge the offer in the core loop
Run the game without opening the purchase choice, then run it with the item. Compare pacing, motivation, difficulty, and recovery so the offer supports play instead of repairing frustration that was added deliberately.
Make the player promise concrete
Describe what changes on screen, how long it lasts, where it appears, and what remains available without it. Replace value labels such as better or premium with rules a player can observe.
Review the moment of choice
Check what the player was doing immediately before the offer and where cancel returns them. The item should arrive after enough context to understand it, but never during a time-critical or emotionally pressured action.
Compare items consistently
Use the same fields for every offer: preview, benefit, ownership or duration, specific Koin amount, and owned state. Consistent cards make differences easier to understand. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.
Keep the first catalog small
Start with one to three clearly different items. A large grid makes it harder to find unclear value, duplicated promises, and missing delivery states. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.
Design owned and unavailable states
A catalog also needs sold, owned, equipped, and unavailable presentations. Do not leave a purchased item looking buyable after reload. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.