The NSketch library aims to provide clean and well documented .Net 2.0 implementation of the most useful sketch-based algorithms. The library is written in C# and targets both Microsoft .Net Framework and Mono.

A sketch is a compact yet approximate representation of some data. Most well-studied sketches quantify the level of approximation through the Probably Approximately Correct (PAC) framework . Intuitively, a typical PAC property indicates that the (approximate) output is within a ε error margin of epsilon with a probability greater than P. If exactness is not a requirement, the approximation tradeoff can provide a huge performance gain against amount of limited error.