Infiltrator.jl is a Julia package that provides an interactive debugging macro, @infiltrate, which acts as a breakpoint with negligible runtime overhead. When triggered, it opens a custom REPL (infil>) allowing developers to inspect local variables, stack frames, module bindings, and evaluate arbitrary expressions. It supports conditional breakpoints, toggling infiltration points on/off, exfiltration of variable values to a store, and integration with Revise.jl for live code updates. The package is designed for development-time debugging and enforces that @infiltrate fails at compile time in package code to prevent accidental commits. It relies heavily on Julia internals (REPL, Core.Compiler, Base.@locals) and maintains compatibility across Julia versions 1.6 through 1.13 via version-adaptive code paths and extensive golden-file test outputs. This is a pure developer tool with no data analysis or research orientation.