A system and technique to specifies patterns to search for in an integrated circuit layout, and specifies proposed replacement patterns. A description file includes specifications for one or more patterns to be searched for. In the description file, for each pattern, there may be one or more proposed replacement patterns. The description file is read. Pattern matches, if any, in a layout are found. A proposed replacement pattern is tested in place of a matched pattern. If acceptable, the proposed pattern may be used to replace the matched pattern.