A two-level matching technique is described. A system can generate a set of index patterns based on a set of library patterns in a pattern library. The pattern library can include patterns that are expected to have problems during manufacturing. Next, the system can use a fast matching process to check if a first-level pattern clip potentially matches one or more index patterns from the set of index patterns. If so, the system can use a detailed matching process to match a second-level pattern clip with library patterns that correspond to the one or more index patterns. Otherwise, the system can report that the first-level pattern clip does not match any library pattern in the pattern library.