This guide to ERRATA, a set of HyperCard-based tools for response analysis and error diagnosis in language testing, is intended as a user manual and general reference and designed to be used with the software (not included here). It has three parts. The first is a brief survey of computational techniques available for dealing with student test responses, including: editing markup that identifies spelling, capitalization, and accent errors and extra, missing, or out-of-order words; pattern matching for rapid identification of specific grammatical errors, keyword searches, and easy specification of alternate answers; and error-tolerant parsing, which puts error diagnosis under control of a grammar and dictionary of the target language. The second section is a user's manual and tutorial guide, describing ERRATA and offering examples of its use. Section three is a reference manual useful to anyone with unusual analysis requirements or wanting to tailor-make responses analyses. Installation and technical information is also included, and complete program code is appended. (MSE)