This is a tool that implements the Earley parsing algorithm as given by Elizabeth Scott and Adrian Johnstone in Recognition is not parsing — SPPF-style parsing from cubic recognisers. The input pane has some sample grammars collected from various parsing papers. Custom grammars and inputs can be supplied in the forms.

Grammars are expected to be in the form Nonterminal ::= term* with spaces between terms and one rule per line. Input is expected to be supplied with no spaces. Rules that can derive the empty string are written with an empty right-hand side (as in S ::= ).