What is GeoProof?
GeoProof is a free, open collection of interactive geometry explorers. Each one lets you drag the figure and watch a classic theorem stay true — turning a static proof into something you can play with.
How to use it
Open any explorer from the home page. Drag the round handles to reshape the figure, and the lengths, angles, and relationships update instantly. Use the toggle buttons to show or hide pieces of the construction, and open the ⓘ “About this theorem” panel on each page for a full explanation — the statement, the formula, special cases, and a little history.
Verified, not just drawn
Every explorer is more than a picture. Before each one ships, its core relationship is re-derived independently and fuzz-tested over hundreds of thousands of random configurations, with errors held to machine precision (around 10⁻¹³). So when a readout says two quantities are equal, they are provably equal — not merely close to the eye.
What’s inside
The explorers span six topics and three difficulty levels, so you can start with the fundamentals or jump to advanced results.
Six topics
Triangles, circles, angles, quadrilaterals, polygons, and transformations — many explorers carry more than one label.
Three levels
Easy foundations, standard high-school theorems, and advanced or olympiad-level results.
Find it fast
Search by name, or filter the grid by topic and level to land on exactly what you need.
Who it’s for
Students building intuition, teachers demonstrating a result live in class, and anyone curious who learns better by doing than by reading.
Built with
Plain HTML, SVG, and JavaScript — no frameworks, no tracking, and no build step. Each explorer is a single self-contained file that loads instantly and keeps working offline.
Open source
GeoProof is open source. The complete source code lives on GitHub — contributions, corrections, and new theorem suggestions are welcome. It is released under the MIT License, so you're free to use, adapt, and share it.
Browse the explorers →