Math practice · reimagined
GCD
Turn GCD into a fight you actually want to win. Every problem is an attack — solve it faster than your opponent and you land the hit.
Ages 4–99+ · no download · plays in your browser · 23 languages
How it works
GCD
Pick a fighter, choose GCD, and trust your numbers. The faster and cleaner you solve, the harder you hit — from gentle early grades all the way to Olympic-level challenges.
GCD means "greatest common divisor" — the biggest number that divides both numbers cleanly, with no remainder.
For 12 and 18: numbers that divide both are 1, 2, 3, 6 — and the biggest is 6. So gcd(12, 18) = 6. Think of the largest tile that could pave two different rooms exactly.
Type the greatest shared divisor.
— Quick answers —
GCD: the short FAQ
- Is GCD free to play?
- Yes. GCD is free to play right in your browser — the whole curriculum, no download, no signup. Paid plans later unlock the full fighter roster, every stage and saved progress.
- Who is GCD for?
- Anyone from 4 to 99+. The early grades stay gentle for beginners, while the higher tiers will make even the confident sweat.
- Do I need to download anything to play GCD?
- Nope. GCD runs in any browser, on a laptop, tablet or phone.
- Can GCD be used in the classroom?
- Absolutely. Teachers run GCD with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.