TreeLine and SlackLine are grammar-based fuzzers for quickly finding performance problems in programs driven by richly structured text that can be described by context-free grammars. In contrast to long fuzzing campaigns to find (mostly invalid) inputs that trigger security vulnerabilities, TreeLine and SlackLine are designed to search for performance problems in the space of valid inputs in minutes rather than hours. The two front-ends use a common back-end. The back-end executes a target application and provides coverage and performance feedback to a search algorithm. It is an extension of the PerfFuzz back-end, which in turn is an extension of AFL. The back-end is packaged as a server running in a separate Unix process to facilitate experimental combinations of different fuzzing strategies. The front end (currently TreeLine for Monte Carlo tree search and SlackLine for genetic search with derivation tree splicing) is responsible for generating inputs to test, as well as recording results. This separation of concerns should facilitate use by other researchers who wish to explore alternatives and extensions of either the front or back ends.