Cthulhu.jl is a powerful introspection tool for exploring the Julia compiler’s method dispatch and type inference system. It allows users to interactively descend into the type-inferred lowered and LLVM IR of Julia functions from the REPL. This makes it ideal for developers who want to optimize performance, debug type instability, or understand how Julia compiles code. Named after the Lovecraftian idea of descending into madness, Cthulhu reveals the "underworld" of Julia compilation.