Sources and attribution
Every problem was written by whoever set the competition it came from, and published by one of three open datasets. None of that is ours.
The datasets
MathNet
Official problem booklets from 47 countries, 1985–2025, with expert solutions. Licensed CC BY 4.0. Dataset.
Omni-MATH
Olympiad-level problems carrying human difficulty ratings, which this site used to calibrate its own scale. Licensed Apache 2.0. Dataset.
NuminaMath 1.5
Competition problems collected from exam papers and mathematics forums. Licensed Apache 2.0. Dataset.
What this site added
Statements and solutions appear as published. What we added is the metadata: a topic for each problem, a difficulty rating, deduplication across the three sources, and the order. Every problem page names its own source and licence.
On the problems themselves
Those licences cover redistributing the collections. They don't cover authorship of the problems, which sits with the competitions named on each page. So the problems and solutions here are free and will stay free; if this site ever charges, it will be for the ordering and the progress tracking. If you set one of these competitions and want a problem taken down, ask and it comes down.