Snowball is a small string processing language for creating stemming algorithms for use in Information Retrieval, plus a collection of stemming algorithms implemented using it.

Snowball was originally designed and built by Martin Porter. Martin retired from development in 2014 and Snowball is now maintained as a community project. Martin originally chose the name Snowball as a tribute to SNOBOL, the excellent string handling language from the 1960s. It now also serves as a metaphor for how the project grows by gathering contributions over time.

The Snowball compiler translates a Snowball program into source code in another language – currently ISO C, C#, Go, Java, Javascript, Object Pascal, Python and Rust are supported.

This repository contains the source code for the snowball compiler and the stemming algorithms. The snowball compiler is written in ISO C – you’ll need a C compiler which support C99 to build it (but the C code it generates should work with any ISO C compiler.)

See for more information about Snowball.

What is Stemming?

Stemming maps different forms of the same word to a common “stem” – for example, the English stemmer maps connection, connections, connective, connected, and connecting to connect. So a searching for connected would also find documents which only have the other forms.

This stem form is often a word itself, but this is not always the case as this is not a requirement for text search systems, which are the intended field of use. We also aim to conflate words with the same meaning, rather than all words with a common linguistic root (so awe and awful don’t have the same stem), and over-stemming is more problematic than under-stemming so we tend not to stem in cases that are hard to resolve. If you want to always reduce words to a root form and/or get a root form which is itself a word then Snowball’s stemming algorithms likely aren’t the right answer.