How to Make a Tower Defense Game with AI: Systems, Balance and Steps

The six systems and the question each one answers

The path: how long is an enemy in danger?

Everything in tower defense comes back to exposure time, the seconds an enemy spends inside your towers' range. For a first map, use one winding path of 40 to 60 tiles on a portrait grid around 12 by 20. Put two or three tight bends in the first half. A tower on the inside of a bend covers two stretches of path at once, so bends are where players feel clever. Avoid a long straight road (every spot along it is equally good, which means no decision) and avoid crossing paths until your second map.

Build spots: where can I put a tower?

You can let players build on any open tile or give them fixed pads. For a first game, pick pads. Eight to twelve pads make balance predictable because you know every possible layout. Make two or three of them great (at bends), most of them decent, and one or two traps that look good but cover little road.

Towers: what problem does each one solve?

Start with four towers, each answering a different enemy:

• Single target (archer, blaster): steady damage, cheap. The workhorse.
• Splash (cannon, mortar): lower damage per hit, but hits a cluster. Answers swarms.
• Slow (frost, glue): little damage, makes every other tower better. Answers fast enemies.
• Long range (sniper, ballista): big hits, slow fire, covers far stretches. Answers armored enemies.

If two towers answer the same problem, cut one. Upgrades come later; one upgrade level per tower is plenty for a first build.

Waves: what am I being tested on right now?

A wave is a list of enemies, their spacing and their order. Each new enemy type should arrive as a lesson: a swarm teaches splash, a fast runner teaches slow, a tank teaches focus fire.

Economy: what can I afford, and when?

Gold comes from kills (a bounty per enemy) and from clearing a wave. The economy sets the pace: too tight and players are punished for one bad placement, too loose and every decision stops mattering.

Lives: how much can I get wrong?

Each enemy that reaches the end costs lives, usually one, more for big enemies. Twenty lives is a forgiving default. Lives are your difficulty dial for mistakes, separate from the wave curve, which is your difficulty dial for skill.

A starting balance you can tune

These numbers are a sensible first pass for a ten-wave map, not a finished balance. Play them, then move them.

Start: 100 gold, 20 lives. Selling refunds 70 percent of what you spent.

Towers:

• Archer: 50 gold, 10 damage, 1 shot per second, range 3 tiles.
• Cannon: 80 gold, 25 damage in a 1 tile radius, 1 shot every 2 seconds, range 3.
• Frost: 70 gold, 3 damage, slows by 40 percent for 2 seconds, range 2.5.
• Sniper: 120 gold, 60 damage, 1 shot every 2.5 seconds, range 6.
• One upgrade each, costing 1.5 times the base price, for plus 50 percent damage.

Enemies:

• Runner: 30 HP, 1.2 tiles per second, 5 gold bounty.
• Grunt: 60 HP, 0.8 tiles per second, 8 gold.
• Tank: 250 HP, 0.5 tiles per second, 25 gold, costs 2 lives if it leaks.
• Flyer: 40 HP, ignores the path and flies straight, 10 gold. Only archer and sniper can hit it.
• Boss: 1,500 HP, 0.4 tiles per second, 150 gold, costs 5 lives.

Wave curve:

1. 8 runners, 1.2 seconds apart.
2. 12 runners.
3. 8 grunts.
4. 10 runners, then 6 grunts.
5. 3 tanks mixed into 8 runners (the first wall: you need focused damage).
6. 14 grunts, 0.8 seconds apart.
7. 20 runners in a tight stream (splash pays off here).
8. 6 flyers with 8 grunts (the first time path coverage is not enough).
9. 5 tanks with 12 grunts.
10. The boss, escorted by 10 runners.

Wave clear bonus: 20 gold plus 5 per wave number. After wave 10, multiply enemy HP by about 1.12 each wave and add one or two enemies.

The check that keeps you honest: required damage per second is roughly the wave's total HP divided by the seconds the wave spends inside your coverage. Wave 1 is 240 HP. If the stream spends about 15 seconds in range of two archers (20 damage per second together), they deal around 300, a small margin. That margin is the feeling of "just made it". Run the same sum for every wave against the gold a player could have by then, and you will catch most spikes before anyone plays.

Build it in Tyrbo, step by step

1. Describe it. One sentence with the theme, the enemies and the twist: "A tower defense where garden gnomes guard a vegetable patch from snails, slugs and a giant beetle boss."
2. Answer the questions. Tyrbo asks a few, each with its best guess already picked: portrait or landscape, fixed pads or open building, how many maps. For a first game, accept portrait, pads and one map.
3. Read the plan before anything is built. You get a title, a pitch, every part of the game and concept art. Check that all six systems are listed. The map is built on a tested tower-defense lane recipe, so the path and pads start from working parts.
4. Play it on your phone. Scan the code and the build runs on your phone. Play three full runs before you change anything.
5. Tune by talking. Say what you saw: "Wave 5 is a wall, cut tank HP to 200" or "nobody builds frost, make it cheaper." Paste the balance above if you want it as your starting point.
6. Ask for your own tools. Tyrbo can write helpers inside your game: a button that skips to any wave, a gold cheat, a slider for enemy HP. Ten minutes of tuning with sliders beats an hour of replaying wave 1.
7. Choose the look last. Pixel art, low-poly 3D, voxel or painted storybook: the tower defense game maker page shows them. Readability first: enemies must stand out from the path.

What to watch when you playtest

• Leaks per wave. One or two leaks on a hard wave is good tension. Five on wave 3 is a broken curve.
• Unspent gold. If players bank 300 gold mid-game, towers are too cheap or there is nothing worth buying.
• One dominant tower. If every winning layout is all archers, the other towers have no job. Give each enemy type a real counter.
• The first loss. Note which wave ends most runs. That wave is either your best moment or your worst.

Mistakes to avoid

• Too many towers too soon. Four with clear jobs beat ten that overlap.
• Linear HP growth. Adding 10 HP per wave feels flat; a gentle multiplier plus new enemy types feels like a climb.
• No breather waves. After a spike, give an easier wave so players can rebuild and feel strong.
• Invisible information. Show range circles on placement, the next wave's enemies, and how many lives a leak costs.

Honest limits

AI can build the systems and change numbers on request, but it cannot tell you whether wave 7 feels fair. That part is you, playing on your phone. Keep the first version small: one map, ten waves, four towers. Tyrbo builds single-player games, so leave co-op and versus out of the plan. When the small version is fun, add a second map. For more on writing the first sentence, read how to write a game prompt.