Germ Guard

A tower defence game set inside the body, for young kids (around age 5). Germs sneak into the body and wiggle along blood vessels towards the heart. Your child builds white blood cells beside the vessels to stop them before they get there.

It has ten levels on a body-shaped map, an endless Germ Party, seven ways to defend, a sneeze, and seven kinds of germ, including a King Germ boss. A Germ Book collects everything your child meets, and stars dress up the heart. A friendly recorded voice explains everything as you go. It has music and vibration, and it can be added to the Home Screen and played offline.

The levels

1. Scraped Knee 🦵: germs come in through one scratch. Only zappers, to learn the game.
2. Runny Nose 👃: germs come out of both nostrils, down two vessels that merge before the heart. Adds the blob nest and the sneeze button.
3. Tummy Ache 🍔: germs come in through the mouth, and a second mouth halfway down sends fast ones on a shortcut. Adds the antibody maker, Wigglers and Chunkies.
4. Lungs 🫁: germs come three ways at once. Adds snot puddles, Corkscrews and Spikies.
5. Itchy Eye 👁️: two vessels run along the upper and lower eyelids round a big blue iris, so your child has to guard both sides.
6. Earache 👂: one long vessel spirals in to the heart in the middle. Pads sit between the rings, so a defender there reaches two rings at once. The germs here are extra tough.
7. Big Fever 🤒: germs pour in through the nose, the mouth and a scratch, all at once, every kind mixed together. The heart is sweating and heat shimmers off the tissue. The last wave brings the King Germ.
8. Cut Finger ✋: a bigger board. Germs get in through two little cuts whose vessels join, then zigzag a long way to the heart, with spots in the bends that reach two stretches at once. Every kind of germ except the King. Adds the platelet plug: tap the vessel to block it.
9. Sore Throat 😮: bigger again. Two ways in from the mouth join and wind down; from wave 2 germs also come in through the nose, which joins further down. Snot puddles help, and two tonsils guard the throat by themselves.
10. Chickenpox 🐔: the biggest board, with the heart in the middle. Germs come from four itchy spots, two above and two below, each pair joining and winding in from its side. Adds the memory cell. The last wave brings two King Germs.

Levels 8 to 10 are big enough that on a small phone they start a little zoomed in; pinch or scroll to see the rest. The first seven boards were also made a little bigger: each entry's vessel is three tiles longer (except the eye, whose entries sit in the corner of the eye), with an extra building spot beside it, and a ring of tissue around the edge.

The map and saving

The title screen is a map: a child's body with a glowing spot for each level (knee, nose, tummy, lungs, the left hand for the finger, the right arm for chickenpox, and next to the head the eye, the ear, the throat and a thermometer for the fever). Tap a spot to play it. Play jumps to the newest unlocked level.

• Winning a level unlocks the next spot. Locked spots show a padlock, and the next one to play glows.
• The best stars for each level (1 to 3, from the hearts left at the end) show under its spot.
• Progress is saved in the browser (localStorage): germguard.stars keeps the best stars per level name, so levels can be added or reordered later. A level opens once the one before it is won. The sound and vibration settings are saved too, and so are the Germ Book (germguard.book), what the heart wears (germguard.dress) and the best Germ Party (germguard.partyBest).
• The map button in the corner during a level, and on the end card, goes back to the map.

Under Play are three more buttons:

• 📖 Germ Book: a page for every germ and every defender, with a picture and a few words. Tap one to hear the voice say what it is. Ones your child hasn't met yet are dark shadows with a "?". Levels already won count as met.
• 🎀 Dress up: stars won on the levels unlock things for the heart to wear in every level: a party hat (3 stars), a bow (6), sunglasses (10), a flower (14), a crown (18) and headphones (22), and colours: pink (8), purple (16) and gold (26). There are 30 stars in all. Locked things show how many stars they need.
• 🎉 Germ Party: opens once the Big Fever is won. An endless game on the Chickenpox board with every defender: the waves never stop, each one bigger and tougher than the last, with a King Germ every fifth wave. When the heart runs out, the card says how many waves your child stopped, and the best ever shows on the 🎉 button.

The defenders

• Germ zapper (a neutrophil, 5 drops): shoots little bubbles at germs in reach.

• Blob nest (a home for macrophages, 6 drops): comes with one blob, and you can train up to 3 (2 drops each). Each blob guards its own spot: the first takes the best tile near the nest (where vessels merge, if there is one), and the others spread out at least two tiles apart, onto different vessels where they can, so one nest covers several stretches instead of crowding one corner. They grab a germ, hold it still and gobble it up. A tired blob lets go, waddles home for a short rest and comes back. Blobs never get hurt.

• Antibody maker (a B cell, 6 drops): throws Y-shaped antibodies that stick on germs. A germ with an antibody on it walks slower and pops faster, and a Spiky loses its armour. The maker picks germs that don't have an antibody yet, Spikies first.

• Snot puddle (4 drops, up to 3 per level, Lungs level): tap the vessel itself to drop one. Every germ that wades through it slows right down.

• Platelet plug (5 drops, up to 2 at a time, Cut Finger and the Germ Party): tap the vessel itself. Germs have to stop at it and chew; the two at the front chew it away, faster for big germs and the King, and then it crumbles and can be built again. Germs queue up behind it, which makes them easy to zap.

• Tonsils (Sore Throat): two pink lumps beside the throat that you don't build. Every 2 seconds they squeeze, which hurts every germ near them. They can't hurt a Spiky until an antibody sticks on it.

• Memory cell (6 drops, Chickenpox and the Germ Party): it remembers every kind of germ your child has ever beaten (saved as germguard.beaten), and a brand-new kind after 3 of them pop on the level. It throws gold antibodies at remembered germs, two at a time: like an orange one, it slows the germ down and breaks a Spiky's armour, but the germ takes more than twice the damage instead of one and a half. It can swap an orange antibody for a gold one. Its two upgrade paths are Reach and Speed (faster, then three at a time).

• Sneeze 🤧 (from Runny Nose on): during a wave the Go button turns into a sneeze button. It blows every germ back down the vessels. Then it needs 40 seconds to recharge, shown as a shadow sweeping round the button. The first time germs get close, a pointing hand and a voice remind your child it's there.

• Upgrades: tap a built defender to improve it. Every defender has two upgrade paths, and each path can be taken twice, so a fully upgraded one has four upgrades. The card shows the path's sign and how far along it is:

Learning about the body

The game names the real body parts and cells, and says what they do:

• First time each defender is placed: its real name floats above it (Neutrophil, Macrophage, B cell, Mucus) and the voice explains what it does. For example: "This is a neutrophil, a kind of white blood cell. Neutrophils rush to germs first and zap them!" The build cards also show the real names, for a parent to read out.

• First sneeze: "A sneeze blows germs out of your nose. Remember to sneeze into your elbow!"

• Platelets, tonsils and memory cells each get a voice line the first time they're used: platelets plug a cut to stop the bleeding, tonsils guard the back of the throat, and memory cells remember germs your body has beaten.

• Every win card shows and reads out a "Did you know?" fact about that body part: why a cut goes red and warm, how snot traps germs, stomach acid and hand washing, the tiny hairs that sweep mucus out of the airways, the germ fighters in tears, what earwax is for, and why a fever helps (plus "rest and drink water").

• Picture cards, only for what a level brings that no earlier level had, shown between waves with one big OK:

  • a new defender gets a picture strip of what it does (zapper ➜ bubble ➜ germ 💥; nest ➜ blob ➜ germ; antibody maker ➜ Y ➜ germ 🐢; snot ➜ germ 🐢) and one short sentence;
  • a new germ gets a card with one row per defender on that level, marked ✓ (works), ✗ (doesn't) or ⭐ (the special answer). The Spiky card, for example, shows the zapper ✗ "bounces off", the nest ✗ "won't grab it", the antibody maker ⭐ "breaks its armour!" and snot ✓ "slows it down". The Chunky card also shows it splitting in 3.

  So the Knee shows the zapper and, before wave 4, the Big Bloop; the Nose the nest; the Tummy the antibody maker, the Wiggler and the Chunky; the Lungs snot, the Corkscrew and the Spiky; the Fever the King Germ before its last wave. The Eye and the Ear bring nothing new, so they show no cards. The words and marks are in DEFENDER_TIP, GERM_TIP and HOW.

Each explanation plays once per visit, like the germ introductions. The words are in LINES (meet-*) and each level's fact.

The germs

Germ	Looks like	What's special
Bloop	green blob	the plain one
Big Bloop	bigger green blob	tough and slow
Wiggler	yellow striped sausage	fast and fragile
Corkscrew	teal spinning spring	too wiggly for blobs to grab
Chunky	lumpy olive cluster	tough; breaks into 3 Bloops when popped
Spiky	purple ball with spikes	shots bounce off, and blobs won't grab it, until an antibody sticks; then its spikes shrink
King Germ	huge grumpy blob with a gold crown	the boss: very tough, slow, tires blobs fast, breaks into 4 Bloops, and costs 3 hearts if it gets through

The first time a new kind shows up in a wave, the voice says what's special about it.

How it plays

• Glowing pads sit beside the vessels. Tap one to see what you can build. The price shows as drop icons 💧, and anything you can't afford yet is greyed out.
• A bubble over each entry shows which germs come out of it next. Tap Go! when ready. Waves never start on their own.
• Popped germs drop energy drops. Tap them to collect, or they fly to the counter by themselves after a few seconds.
• Each cleared wave adds 3 bonus drops from the heart. Drops are scarce, so where and what you build matters.
• The heart has 5 hearts of health. A germ that reaches it costs one (and earns the heart a plaster).
• New building spots open up as a level goes on: before wave 3 and again before wave 5, an extra pad springs up with sparkles and a chime, and the pointing hand shows where it is. The later one is the better spot, ready for the hardest wave. In the maps they're the letters c and e (any of b to e opens before wave 2 to 5).
• The heart's health shows in three places: the hearts in the top bar, a row of hearts floating over the heart itself, and the heart: a plaster for every germ that got through, and a face that goes from smiling to straight to worried. Each hit floats up a "💔 -1" (or -3 for the King Germ). On its very last heart, the heart races and both heart rows pulse red.
• During a wave, the 2× button next to the sneeze makes everything run twice as fast; tap again for normal speed. It stays on for later waves until turned off.
• If all 5 are gone: "Achoo!" and Try again replays that wave. Every defender and drop is kept and the heart is refilled.
• Clear all 5 waves to win. You get 1 to 3 stars depending on how many hearts are left.
• A pointing hand and a spoken voice show where to tap first on each level.
• Zoom and scroll: pinch (or use the mouse wheel) to zoom in and out, and drag the board to scroll around it. A quick tap still builds; a finger has to move a little before it scrolls instead. While zoomed in, a 🔍 button under 🏠 glides back out to the whole board. Each level starts showing the whole board, unless the board is so big that its tiles would be tiny: then it starts zoomed in on the first spot to build on. When a new building spot opens off screen, the view glides over to it, and the bubbles for entries that are scrolled away stay at the edge.
• 🏠 in the corner goes back to the list of all games.

Sound, music and vibration

• Voice: every spoken line is a recorded clip (see the audio credits below): level introductions, wins, what each new germ does, and hints. Lines that come one after another queue up instead of cutting each other off. If a clip can't load (for example when the game is opened straight from disk), the browser's own voice says it.
• Sound effects: the sneeze, a blob's chomp, a germ's pop, the heart's bonk, the King Germ's arrival and the win fanfare are recorded clips. Everything else (shots, building, drops and so on) is synthesized with Web Audio, and each recorded effect has a synthesized fallback.
• Music is made up in code, no recordings. Every body part has its own little tune: a chiptune hop for the Knee, sniffly plucks for the Nose, a wobbly polka for the Tummy, a soft flute for the Lungs, twinkly bells for the Eye, an echo for the Ear and a hot, jumpy one for the Fever. The map has its own tune, and the King Germ has a grumpy minor-key march. While building a tune plays slow and gentle; in a wave it speeds up with drums and a bouncier bass. It dips while the voice talks and stops for the win and lose jingles.
• The 🎵 button next to Play turns the music off (sounds and voice stay on), and is remembered.
• The 🔊 button mutes everything: effects, music and voice. Audio starts with the first tap, and on an iPhone the silent switch mutes it.
• Vibration comes on building, upgrading, the sneeze, a germ reaching the heart, the King Germ arriving, and winning or losing. It works on Android. On iPhone (iOS 18+) it uses the system tap trick from Matma, which only works right after a touch. The 📳 button next to Play turns it off, and it only shows on devices that can vibrate.
• The screen gives a little shake when the heart is hit, on a sneeze, and when the King Germ arrives.

Home Screen and offline

The game has a web app manifest, icons (icon.svg, plus icon-180.png and icon-512.png rendered from it in headless Chrome) and a service worker (sw.js, the same as the other tb-x games apart from its cache prefix germ-guard-). After one visit it works without internet, including three.js and the font. Because it serves from the cache first and refreshes in the background, a new version shows up one launch late.

Running it

Serve the folder and open it in a browser:

python -m http.server 5209

Then go to http://localhost:5209/. Opening index.html straight from disk mostly works too.

For testing, add #debug to the URL. The browser console then has a gg handle:

• gg.loadLevel(i) loads a level.
• gg.build(padIndex, 'zapper' | 'nest' | 'antibody'), gg.upgrade(padIndex, path) ('reach', 'power', 'bite', 'energy' or 'speed'; without a path, the one that makes it bigger), gg.train(padIndex) and gg.trap(col, row) build and improve defenders.
• gg.spawn(kind, entry, dist) adds a germ.
• gg.sneeze() sneezes.
• gg.unlockAll() opens every level on the map, and gg.goHome() goes back to the map.
• gg.step(seconds) runs the game forward without waiting.
• gg.game.instant = true makes drops count straight away instead of flying to the counter.

Tuning knobs

These are at the top of the script in index.html:

Knob	What it does	Now
HEART_SPARKLES	germs the heart can take before the wave is replayed	5
WAVE_BONUS	bonus drops after each cleared wave	3
DROP_AUTOCOLLECT_S	seconds before an untapped drop collects itself	4
SHOT_SPEED	zapper shot speed, in tiles per second	9
BUILDS	for each defender: its cost, and its two upgrade paths (tracks), each with a label, sign, the drops for its two steps (costs) and the numbers at steps 0-2 (steps)	see the upgrades table above
BUILDS.zapper	Reach: range 2.7, 3.0, 3.3 tiles; Power: seconds between shots / damage 0.85/1, 0.6/1, 0.8/2	5 drops
BUILDS.nest	guard reach 2.3 tiles; Bite: blob damage per second 1.8, 2.4, 3.0; Energy: blob stamina 8, 11, 14	6 drops
BUILDS.antibody	Reach: range 2.8, 3.1, 3.4 tiles; Speed: seconds between throws / germs per throw 1.4/1, 1.0/1, 0.9/2	6 drops
TAG_SLOW, TAG_DAMAGE	speed and extra damage for a germ with an antibody on it	0.7, 1.5
AB_SPEED	antibody flying speed, tiles per second	6
MUCUS_COST, MUCUS_MAX, MUCUS_R, MUCUS_SLOW	snot price, puddles per level, reach in tiles, speed inside it	4, 3, 0.6, 0.4
PLUG_COST, PLUG_MAX, PLUG_HP, PLUG_CHEW	platelet plug price, plugs at a time, how much chewing it takes, chewing per second per germ (times its bite)	5, 2, 36, 2
TONSIL_R, TONSIL_RELOAD, TONSIL_DAMAGE	tonsil reach in tiles, seconds between squeezes, damage per squeeze (tonsils are t on a map)	1.7, 2, 1.5
MEMORY_KILLS, MEMORY_DAMAGE

Each level in LEVELS has its own map, colours (palette), entry look (entry: one style, or a list with one per entry), starting drops (startEnergy), allowed defenders (builds, plus mucus and sneeze switches), the first-tap hint, an optional toughness that multiplies every germ's health (Knee 1.35, Nose 1.25, Tummy 1.1, Earache 1.6, Finger 2.15, Throat 1.5, Chickenpox 1.4), its spot on the map, and waves. The intro and win words are also voice lines, so changing them means recording new clips. A wave is a list of groups: germ kind, how many, seconds apart, an optional start delay, and which entry they come from (from, 0 = the map's 1). Maps can be any size: the shadows grow with the board, and a board too big to show at a readable size on a phone starts zoomed in and is scrolled around (a 30 × 30 test board worked).

Balance as tested with simulated play

Tested on 2026-10-09 with an automatic player in three styles. It plays each level the way a child might, and uses Try again (which keeps everything built) when a wave is lost:

• Thoughtful keeps building a mix (zappers first, a nest, then antibody makers, and an antibody maker straight away when Spikies are in the next wave), drops snot where vessels merge, takes the new spots when they open, and spends spare drops on upgrades. It also sneezes when germs get close.
• Lazy builds three defenders and stops.
• Zappers only builds and upgrades nothing but zappers.

The numbers are hearts left after each wave; ✗ is a lost wave that was tried again.

Level	Thoughtful	Lazy	Zappers only
1 Scraped Knee	won, 5 5 5 5 5	lost at wave 3	(same as thoughtful)
2 Runny Nose	won, 4 4 4 4 4	lost at wave 3	won, 5 5 5 5 5
3 Tummy Ache	won, 4 4 4 4 4	lost at wave 2	won, 5 5 5 5 5
4 Lungs	won, 5 5 5 5 5	lost at wave 3	lost at wave 3 (Spikies)
5 Itchy Eye	won, 5 4 4 4 4	lost at wave 3	lost at wave 4 (Spikies)
6 Earache	won, 5 5 5 5 5	lost at wave 2	lost at wave 4
7 Big Fever	won, 4 4 4 4 4	lost at wave 2	lost at wave 3 (Spikies)
8 Cut Finger	won, 5 5 5 5 4	lost at wave 2	lost at wave 4
9 Sore Throat	won, 5 5 4 4 3	lost at wave 2	lost at wave 3
10 Chickenpox	won, 5 5 5 5 2	lost at wave 1	lost at wave 3

Tuning so far: the early levels got tougher germs and busier last waves, and the King Germ went from 130 to 340 health. After the boards grew, the Itchy Eye needed 20 starting drops (was 18), the Big Fever 25 (was 23), and the Tummy Ache's Wigglers now come out of the short second entry a little later. In the Big Fever the King Germ gets about 71% of the way to the heart. In Chickenpox one of the two Kings nearly makes it (98%), and that wave usually costs the heart 3. The Knee is still easy on purpose, as the tutorial; stopping early loses everywhere, and the Spiky levels can't be won without antibodies.

With the platelet plug, the tonsils and the memory cell added, the thoughtful player also drops plugs on the Cut Finger once germs are coming, and builds a memory cell on Chickenpox from wave 2. The first memory cell only remembered germs popped on the same level, so on Chickenpox it was worse than the zapper it replaced and the King wave was lost; now it remembers every germ ever beaten (the King too, from the Big Fever) and throws gold antibodies. The Germ Party lasted 4 to 14 waves in six simulated runs, usually ending at the first King (wave 5) or around wave 14.

The new big levels first had long, separate vessels with spots that each reached only one of them, and even the thoughtful player lost there. Joining the entries into a shared vessel that zigzags, with spots in the bends, fixed that: now a defender in the right place covers two stretches, as on the first seven levels. The Earache's germs have toughness: 1.6 and a gentler first wave, after the first version (2.5× health, a 16-germ first wave) turned out to be unwinnable in wave 1.

Made with

Plain HTML and JavaScript. three.js 0.170.0 from jsDelivr draws the isometric board, and every model is built from simple shapes in code. Music and most sounds are synthesized with Web Audio; the voice and six sound effects are ElevenLabs clips.

Audio credits

Voices and sounds: elevenlabs.io. The credit also shows on the game's title screen and end card. All clips were made on 2026-10-09 with an ElevenLabs free plan, so they may only be used non-commercially and must credit ElevenLabs. The game must stay free (no ads, payments or sponsorship), and the clips are not covered by any licence on this game's code.

Every clip is listed below.

Spoken lines (69 clips): ElevenLabs Text to Speech, stock voice "Jessica" (Playful, Bright, Warm), model Eleven Multilingual v2, free plan, made 2026-10-09. The words are also in LINES, GERM_HELLO and each level's intro, win and fact.

File	Words
say-intro-knee.mp3	"Oh no, a scratch on the knee! Germs are sneaking in. Tap a glowing spot to build a germ zapper."
say-win-knee.mp3	"Hooray! You stopped all the germs. The knee is all better!"
say-intro-nose.mp3	"Achoo! A runny nose! Germs are coming from both sides. Try the new blob nest: its blobs grab the germs and gobble them up!"
say-win-nose.mp3	"Hooray! No more sniffles!"
say-intro-tummy.mp3	"Uh oh, a tummy ache! Germs came in with the food. New: the antibody maker. Its antibodies stick on germs, so they slow down and pop faster!"
say-win-tummy.mp3	"Hooray! The tummy feels great!"
say-intro-lungs.mp3	"Cough cough! Germs are in the lungs, coming three ways. New: tap the vessel to drop sticky snot there. Germs get stuck in it!"
say-win-lungs.mp3	"Hooray! Big deep breaths!"
say-intro-eye.mp3	"Blink blink, an itchy eye! Germs are sneaking along both eyelids. Guard the top and the bottom!"
say-win-eye.mp3	"Hooray! The eye is bright and clear!"
say-intro-ear.mp3	"Ouch, an earache! The germs go round and round the ear to reach the heart. Build in between the rings to zap two at once!"
say-win-ear.mp3	"Hooray! The earache is gone!"
say-intro-fever.mp3	"Oh no, a big fever! Germs are coming from the nose, the mouth and a scratch, all at once. Use everything you have!"
say-win-fever.mp3	"You did it! The fever is gone, and the heart feels great!" (re-recorded once levels came after it)
say-intro-finger.mp3	"Ouch, a cut on the finger! Germs are getting in through two little cuts. The way to the heart is long, so build all along it!"
say-win-finger.mp3	"Hooray! The finger is all healed!"
say-intro-throat.mp3	"Ow, a sore throat! Germs are coming in through the mouth, and soon through the nose too. Sticky snot helps here as well!"

Sound effects: ElevenLabs Sound Effects, free plan, made 2026-10-09.

File	Sound	Length
sfx-sneeze.mp3	cartoon sneeze, "ah... ah... achoo!"	1.8 s
sfx-chomp.mp3	a blob's squishy chomp	0.6 s
sfx-pop.mp3	a germ popping like a slime bubble	0.5 s
sfx-ouch.mp3	a soft cartoon bonk when a germ reaches the heart	0.8 s
sfx-king.mp3	the King Germ's goofy grumble and rumble	2.5 s
sfx-win.mp3	short victory fanfare with chimes	2.5 s