🖍️ Coloring Corner

A coloring-page kiosk for kids. They browse or search a library of 240 coloring pages, tap their name, and the page comes out of your printer. Each kid gets a few pages a day, so the printer doesn't run out of paper by lunch.

Pick who's coloring	Off to the printer

• 240 pages, ready to go: 12 categories (animals, dinosaurs, trucks, space, unicorns, holidays...) x 10 subjects, each in an easy version (ages 3-5, chunky outlines) and a detailed one (ages 6-10).
• Safe by design: no web search and no AI at runtime. Kids only ever see the pages in the library.
• Daily allowance: each kid gets limit pages per rolling 24 hours (3 by default). When they're out, the screen tells them when the next one unlocks. A failed print doesn't count.
• Grown-up panel: hold the "Coloring Corner" title for 3 seconds and enter the PIN to give a kid an extra page, reset their count, or see recent prints.
• Two ways to print: straight to a CUPS print queue (best for a kiosk tablet), or through the browser's own Print dialog (no print server needed).
• Small and boring on purpose: one Node.js server, no npm dependencies, no database (an append-only log file).

Quick start (Docker)

git clone https://github.com/2shepard2/coloring-corner.git
cd coloring-corner

# 1. The pages (75 MB) live in a release download, not in git:
curl -LO https://github.com/2shepard2/coloring-corner/releases/download/v1.0.0/coloring-corner-library-v1.zip
unzip coloring-corner-library-v1.zip            # creates ./library

# 2. Your kids and your settings:
cp config/kiosk.example.json config/kiosk.json   # edit the names, emoji, colors, limit
cp .env.example .env                             # edit timezone and printer settings

# 3. A grown-up PIN (4-8 digits):
mkdir -p data secrets
shuf -i 1000-9999 -n1 > secrets/admin_pin && cat secrets/admin_pin
sudo chown -R 10240:10240 data secrets/admin_pin && sudo chmod 400 secrets/admin_pin

# 4. Go:
docker compose up -d --build
curl -s localhost:3240/health

Open http://<your-server>:3240/ on the kids' tablet or computer.

The container runs as user 10240, which is why data/ and the PIN file are handed to that user.

Printing

PRINT_MODE=cups (recommended for a kiosk)

The server sends each page to a CUPS print queue, and CUPS scales it onto the paper. Kids tap "Yes, print it!" and walk over to the printer. There are no dialogs to get lost in.

• Any Linux box, Raspberry Pi or NAS running CUPS works. Add your printer there first and print a test page.
• Find the queue name with lpstat -h your-cups-host:631 -p.
• Set CUPS_SERVER, CUPS_QUEUE and PAPER_SIZE (Letter or A4) in .env.
• CUPS must accept jobs from the Coloring Corner server's address (CUPS' "Share printers" / Allow settings).
• Test without paper: PRINT_DRY_RUN=1.

PRINT_MODE=browser (no print server)

The page is counted against the kid's allowance, and then the browser's Print dialog opens with only the picture on the page. This is the easiest option on a laptop or desktop already set up to print. It doesn't work inside the Android kiosk app below (Android's WebView has no print dialog); use CUPS there.

Settings

config/kiosk.json:

Key	What it does
limit	Pages per kid per rolling 24 hours
kids	name, emoji and color for each kid (any number of kids)
synonyms	Extra search words per category

.env:

Variable	Default	What it does
TZ	UTC	Your timezone, for "more at 3:15 PM"
PORT	3240	Web port
PRINT_MODE	cups	cups or browser
CUPS_SERVER	localhost:631	CUPS host and port
CUPS_QUEUE	(none)	Required for cups mode
PAPER_SIZE	Letter	Letter, A4, ...
GAMES_URL	(none)	Shows a 🎮 Games button linking to another kids' site
PRINT_DRY_RUN	0	1 = pretend to print

The PIN comes from the file in ADMIN_PIN_FILE (Docker) or the ADMIN_PIN variable. With neither set, the grown-up panel is off. Five wrong tries lock it for five minutes.

Running without Docker

Node.js 20 or newer, plus lp (package cups-client) for CUPS mode:

LIBRARY_DIR=./library CONFIG_FILE=./config/kiosk.json ADMIN_PIN=1234 \
  PRINT_MODE=browser node server.js
npm test

The tablet (optional Android kiosk app)

Any tablet browser works. For a "kids can't wander off" setup, android/ has a tiny kiosk app: a full-screen page with no address bar that can be set as the tablet's Home app, so the Home and Back buttons stay in Coloring Corner. It asks for the server address on first launch. Grown-ups get out through the grown-up panel: ⚙️ Tablet settings opens Android settings (choose another Home app there), and 🔗 Server address changes the address.

There's no prebuilt download, because an app has to be signed with a key, and that key should be yours. Building it needs a JDK, aapt, zipalign, apksigner, an Android API 30 android.jar and Google's R8/D8:

keytool -genkeypair -keystore kiosk.jks -alias kiosk -keyalg RSA -validity 10000
ANDROID_JAR=/path/to/android.jar R8_JAR=/path/to/r8.jar \
  KEYSTORE=kiosk.jks KEYSTORE_PASSWORD_FILE=/path/to/password.txt android/build.sh
adb install android/build/coloring.apk

It runs on Android 8 and newer, and was built for a cheap 8" Android 10 tablet. On that tablet, the page sometimes stayed blank after the app was reinstalled until the tablet was restarted.

Make your own pages

The library was drawn by image models (about $6 for all 240 through OpenRouter), then checked by eye, with the duds redrawn. To add or change pages, edit scripts/subjects.json and run:

pip install pillow
OPENROUTER_API_KEY_FILE=~/openrouter.key python3 scripts/build_library.py 8   # 8 = dollar cap

It only draws pages that are missing, so you can stop and rerun it, and it stops at the dollar cap. Easy pages use black-forest-labs/flux.2-klein-4b and detailed ones use google/gemini-3.1-flash-lite-image; override them with EASY_MODEL / DETAILED_MODEL. Look over what it draws before kids see it, then restart the server to load the new pages.

About the pages

The pages were made with AI image models. You're free to print, share and modify them. They come as-is, like the code (MIT license).