Fuzzing, or random testing, is an increasingly popular testing technique.
The power of the approach lies in its ability to generate a large number of useful test cases without consuming expensive manpower.
Furthermore, because of the randomness, it can often produce unusual cases that would be beyond the awareness of a human tester.
In this paper, we present Grammarinator, a general purpose test generator tool that is able to utilize existing parser grammars as models.
Since the model can act both as a parser and as a generator,
the tool can provide the capabilities of both generation and mutation-based fuzzers.