Tower Defense Strategy: Build, Upgrade and Survive Endless Waves (2026)

1. Read the map before you place anything

The map is 16 x 16 cells and the path runs from the top-left cell to the bottom-right cell. Monsters follow that path, and any tower or wall you place on a cell becomes an obstacle: the build refuses a placement that would cut the entrance off from the exit, so you cannot wall the map shut, but you can still narrow the corridor and force monsters to walk a longer route. That extra distance is the whole game — every tower you own gets more shots the longer a monster stays in range.

Decide your corridor in the first ten seconds, before wave 1 arrives. A diagonal band from the top-left to the bottom-right leaves room for two or three rows of towers on each side; a straight horizontal-then-vertical path is easier to defend but gives monsters fewer steps inside your kill zone.

2. Spend the opening $500 on range, not on damage

You start with $500 and waves 1 and 2 send a single slow monster. The cheapest tower is the LMG at $100 with range 5 and damage 5; the Cannon at $300 hits harder but reaches only 4 cells. Two LMGs placed on opposite sides of the first corridor segment cover the whole early path and leave $300 in the bank for wave 3, which sends two monsters. A single Cannon is stronger on paper but a lone tower with no backup loses to any monster that walks past its range.

Walls cost $5 and have 500 shield. They are not damage dealers; they are the cheapest way to bend the path. Dropping a Wall one cell off the straight diagonal forces monsters to detour around it, and that detour is usually worth more than $5 of extra tower damage.

3. Match the tower to the job

• LMG ($100, range 5, damage 5, speed 3) — the workhorse. Longest reach for the price, fast enough to chip every monster that passes. Buy these first and upgrade them last.
• Cannon ($300, range 4, damage 12, speed 2) — the mid-game punch. Higher per-shot damage than the LMG but slower and shorter-ranged; place it where monsters are forced to slow down, not on a straightaway.
• HMG ($800, range 3, damage 30, speed 3) — the closer. Shortest range of the five, highest damage per shot; it earns its price only when monsters are funnelled into a two-cell-wide choke.
• Laser gun ($2000, range 6, damage 25, speed 20) — the late-game answer. Longest range and a very fast fire rate, but it costs four times the Cannon. Buy one when waves start sending 20+ monsters and your LMGs cannot clear them.
• Wall ($5, shield 500) — not a weapon, but it blocks monsters and shapes the path. It has no upgrade path that matters; sell it for $1 if you need the cell back.

The range numbers are in cells, so a Cannon covers a 9 x 9 square centred on its cell and an LMG covers 11 x 11. Place a tower so its range overlaps the corridor for as many cells as possible, not so it sits on the corridor.

4. Upgrade is 75% of what you paid, so upgrade deliberately

Upgrading a tower costs floor(0.75 x the money you have put into it so far), and selling it returns floor(0.5 x that same amount). Those two numbers are the reason to be picky:

• Upgrading a $100 LMG costs $75 and raises its damage by 20% (the default upgrade rule is 1.2 x per level). After five upgrades you have spent $375 on top of the $100 and the tower is doing roughly 2.5 x its starting damage.
• Selling that same tower returns only $250, so an upgrade you regret costs you $225 of lost value.
• The Cannon and HMG use custom upgrade rules (1.2 x and 1.3 x per level respectively) and the Laser gun 1.2 x; the Cannon's rule switches to 1.3 x after level 10.

The practical rule: upgrade a tower only after it has killed at least one monster per wave for three waves running. If a tower is not firing, its money is better spent on a new tower in a better cell. Selling is a last resort, not a strategy.

5. The first ten waves are a script; learn them

Waves 1 to 10 are fixed:

Monster 1 is the basic type (life 50, speed 3, damage 1, no shield). Monster 2 is faster (speed 6, damage 2). Monster 3 is the speed type (speed 12, life 50, damage 3). Use waves 1-6 to build your corridor and your first two or three towers; by wave 7 you should have at least four towers and a clear kill zone. Wave 10 is the last scripted wave — from wave 11 onward the build generates floor(wave ^ 1.1) monsters, capped at 100 per wave, and the difficulty multiplier starts climbing.

6. Monster stats decide which tower to buy

The nine monster types, with their base stats (before the difficulty multiplier):

Two consequences:

• A fast monster (speed 12+) spends less time in any tower's range, so a fast tower (HMG speed 3, Laser speed 20) is worth more against it than a Cannon (speed 2).
• A shielded monster (shield 20) shrugs off single hits, so the Cannon's 12 damage and the Laser's 25 damage are better than the LMG's 5. Against monster life (500 HP) and monster shield-life (300 HP, shield 15) you want the highest damage per shot you can afford.

The difficulty multiplier starts at 1 and rises: x1.05 for waves under 5 when the previous wave dealt no damage, x1.2 for waves 5-9, x1.1 for waves 10+ when the previous wave dealt no damage, and it is cut back (x0.6 to x0.9) when the previous wave dealt 10-50+ damage. So a bad wave makes the next one easier and a clean wave makes the next one harder. Do not read a single easy wave as a sign you are ahead.

7. Use the three-second gap between waves

After a wave clears, the build waits 72 frames (3 seconds at 24 fps) before spawning the next one, and it recovers life during that gap: +5 if the wave number is a multiple of 5, +10 if it is a multiple of 10, capped at 100, but only when the previous wave dealt less than 10 damage. That gap is your only chance to build and upgrade without monsters on the map. Spend it, every wave, even if you think you are fine — a tower placed during the gap is firing by the time the next wave's first monster reaches it.

The gap is also when the difficulty multiplier is applied, so the number you see in the log ("wave N, last wave damage = X, difficulty = Y") is the multiplier you are about to play against.

8. Do not let the path block itself

The build checks, before every placement, whether the new tower or wall would disconnect the entrance from the exit. If it would, the placement is refused with "Can't build here, it will block the way". A placement that does not block the path but would trap a monster already on the map is also refused ("Can't build here, some monster will be blocked"). Read those messages: they are telling you that your corridor is too tight, not that the cell is invalid.

The practical consequence is that you cannot build a wall maze. You can only narrow the path to two or three cells wide, which is enough for a kill zone but not enough for a labyrinth. Plan for a funnel, not a maze.

FAQ

Why does the game never end?

The mode is endless survival: waves keep coming until your life reaches 0, and there is no final wave or win screen. The bridge emits game_load, game_start and game_60s only — there is no win or restart event, because neither applies. Treat your best wave as your score.

What does the panel show?

Money, score, life, number of buildings, number of monsters on the map, and the current wave. Life is capped at 100 and recovers between waves as described above. Score increases when a monster is killed (floor(sqrt(damage dealt)) per hit).

Can I pause?

Yes. The pause button freezes the map and the monsters; the restart button clears the map, resets life, money and score, and starts wave 1 again. Restarting fires the standard restart event through the bridge only if a run had started.

How do I play on a phone?

Every action is a tap: tap an empty cell to enter build mode, tap a tower type to place it, tap an existing tower to upgrade it, tap the panel buttons for pause, speed and restart. Swipe is not used because every target is a tap target. The canvas scales to the screen and the touch shim prevents the page from scrolling while you play.

Is there a way to practise a layout?

The build does not expose seed or difficulty parameters in the URL the way some of this site's other games do. The only way to repeat a run is to memorise the placement order; the first ten waves are fixed, so a layout that survives wave 10 can be reproduced exactly.

Where can I play it?

Right on this site's Tower Defense page. The game is a Playnesta-hosted adaptation of the open-source html5-tower-defense project (upstream commit e3e009c, MIT, Copyright (c) 2017 oldj): Playnesta self-hosted the prebuilt English bundle with no gulp or build chain, stripped the upstream site shell, and added a standalone analytics bridge, a touch shim and responsive CSS. The upstream LICENSE.txt is included in the package. Tower Defense is a generic descriptive term and no trademark claim is made.