Welcome back: designing offline progress

The defining promise of the genre is that the game keeps going without you. Making that promise feel good takes three decisions.

1. Compute it from the clock, not from ticks

A browser tab in the background, a closed phone app or a laptop asleep in a bag all stop running code. So offline progress can't be simulated tick by tick; it is calculated on return from the time that passed. That makes clock handling a real concern: a device clock set backwards should give nothing, and a clock jumped years forward should not hand out years of income.

2. Cap it, then let players raise the cap

A cap stops the best strategy from being “never open the game”. It also creates something to buy: upgrades that extend the cap are some of the most-loved purchases in idle games because they reward the way people actually play.

3. Say what happened

The “while you were away” card is the game's handshake. It names the time, the earnings and, ideally, what you can now afford. A number with no next step is a statistic; a number with a next step is a reason to play.

On this site

Tidekeeper runs in a dock while you browse, so it rarely needs offline math here, but close the tab and it falls back to exactly this model. Try it: start the reef, close the tab for a few minutes, then come back.