Troubleshooting Software-Defined Networks requires a structured approach to detect mistranslations between high-level intent (policy) and low-level forwarding behavior, and a flexible on-demand packet tracing tool is highly desirable on the data plane. In this paper, we introduce a Layer 2 path tracing utility named PathletTracer. PathletTracer offers an interface for users to specify multiple Layer 2 paths to inspect. Based on the Layer 2 paths of interests, PathletTracer then accounts paths with identifiable IDs, and installs a set of flow table entries into switches to imprint path IDs on the packets going through. PathletTracer re-uses some fields in packet headers such as the ToS octet for recording path IDs. To efficiently carry imprints using limited bits, PathletTracer uses an encoding algorithm motivated by the calling context encoding scheme in the software engineering domain. With k bits for encoding, PathletTracer is able to trace more than 2 k paths simultaneously