Build this kind of game
Make movement add up identically on every player's computer
When every machine calculates the same moves, tiny differences in how decimals are rounded can add up until characters stand in different places. Whole-number maths avoids that, but the obvious way of dividing breaks for negative values and can overflow. Here are the safe building blocks.
Let a town's population grow and shrink toward what homes and food can carry
A town should fill its houses gradually and shrink gently when food runs short, instead of jumping to the limit or flickering up and down by one citizen every second. Here is a rule for the next population number that never overshoots and always arrives.
Share out too little power so the hospital keeps running and no unit goes missing
When a city produces less than it uses, something must go dark. Dividing it evenly darkens the hospital together with the lamps, and dividing it by percentages leaves a unit of power lost or created in the rounding. Here is a fair rule that adds up exactly.
Find production chains where a tool is needed to make the tool and nothing ever starts
In a game with workshops, a mine can need a pickaxe while the pickaxe needs the ore from the mine. On paper everything is connected, in play nothing moves and the player cannot tell why. Here is a check that shows which workshops can never run from the start.
Stop slow income from rounding to zero or drifting away over a long game
A tiny income per tick, such as a third of a coin, either never arrives or slowly gains and loses cents, so two players with the same city end up with different treasuries. Here is how to count so that nothing is lost, however the time is cut into pieces.
Find the buildings that are cut off from the rest of your city by a gap in the road
A farm can sit right next to a road and still deliver nothing, because that road never reaches the town. Here is a check that follows the roads from the start point and lists every building that is not truly connected, so the game can warn the player.
Show a turn order where a fast unit really acts twice as often as a slow one
Games with a visible turn bar promise that speed matters, but the bar goes wrong when two units are due at the same moment: the order jumps, or a unit loses a turn after many rounds. Here is a way to line up the next turns that stays exact however long the battle lasts.
Check that every player of a generated map starts with about the same amount nearby
A map made by chance can give one player a forest and a gold mine next door and another player bare ground. Players notice within a minute and quit. Here is a check that adds up what lies around each starting point and tells you whether the map is fair enough to use.
Make sure that if your archer sees the enemy, the enemy sees the archer
On a square map, a line drawn between two units can run slightly different ways depending on which end you start from. The result is one side seeing a target that cannot see back, and players smell cheating. Here is how to draw the line so the answer is the same from both ends.
Tell tap, hold, drag, pan and pinch apart on a phone strategy game
On a phone, one finger can mean select, hold for a menu, or scroll the map, and two fingers can mean zoom or move. A shaky tap becomes a drag, or a zoom moves the map as well. Here is how to classify a touch so these things do not fight each other.
Let players undo a move without letting them reroll a missed shot
Undo is a kindness in a thinking game, until someone discovers they can miss, undo, and try again until the dice are kind. Here is how to keep undo for moves but make a repeated attack give the same result, and when to close the door for good.
Find upgrades in your city builder that never pay for themselves
If one upgrade costs far more than the extra income it brings, nobody buys it, and if another pays back in a minute, everybody buys only that. Here is a quick check over a whole list of levels that shows how long each one takes to earn its price back and marks the odd ones.