About MentalForge

MentalForge builds mental-calculation fluency — the ability to work with numbers quickly in your head. It is one of the two classic mind-sport skills (with memory) that the library was missing.

Four ways to practise

• Sprint — pick add, subtract, multiply or divide and a difficulty, then work eight questions in your head. An abacus pictures each number so you can see it. Try to beat your own best time.
• Trick lab — learn mental-maths shortcuts (multiply by 11, square a number ending in 5, subtract from a round number) worked out step by step, then try one yourself.
• Skill Ladder — one skill at a time: a worked example, then a few to do yourself; get four in a row to clear a rung. No clock.
• Trust the Mental-Math Bot? — a bot answers some sums; you check which answers to trust, and see where a machine's mental maths goes wrong.
• Where the tricks come from. Multiply-by-11 and subtract-from-a-round-number are in Jakow Trachtenberg’s system (written up in a 1960 book by Ann Cutler and Rudolph McShane). A 1965 book called Vedic Mathematics, by Bharati Krishna Tirtha, also teaches tricks like these. Despite its name, historians have found its rules are not in the Vedas.

How it works — and stays honest

• A real engine grades every answer. Every question and every answer is computed by a deterministic maths engine — no AI is ever near the arithmetic, so the grading can’t be wrong.
• On-device, no accounts. Your practice and your personal best live in this browser only; nothing is sent anywhere (no login, no data leaves the device).
• Calm by design. No stress clock, no streaks to protect, no leaderboard. The score you chase is your own previous best.

Honest note: mental calculation is a real, learnable skill worth practising. It is a maths skill — not a shortcut to being “smarter” in general.