This paper describes the development of Tango, an automatic generator of backtracking trace analysis tools for single-process specifications written in the formal description language, Estelle. A tool generated by Tango automatically checks the validity of any execution trace against the given specification, and supports a number of checking options. The approach taken was to modify an Estelle-to-C++ compiler. Discussion about nondeterministic specifications, multiple observation points, and on-line trace analysis follow. Trace analyzers for the protocols LAPD and TP0 have been tested and performance results are evaluated. Issues in the analysis of partial traces are also discussed.