A system and method for reverse engineering of pattern string validation scripts is presented. A pattern engine receives an input string from a developer or a database, and generates a pattern string based upon the input string and strictness preferences. The strictness preferences identify how much to constrain generated pattern elements that are included in the pattern string. Once the pattern engine generates the pattern string, the pattern engine creates a user-friendly format string that is used by a developer to assess pattern string adjustments. The pattern engine may operate in a single mode or a multi-mode. In a single mode, the pattern engine uses a single input string to generate a pattern string. In a multi-mode, the pattern engine uses multiple input strings, typically from a database, to generate a pattern string.