The free software is an open box in theory, but the complexity of the code may turn it into a closed box in practice. GDB contains several hundred thousand lines of code; if you are not part of the community that has developed it for the last ten years, or have not followed closely the mailing lists, adding a new feature is an almost impossible task.

By contrast, ZeroBugs can be customized, using either C++ or Python. The debugger provides two set of APIs:

the ZDK (Zero Development Kit), a collection of C++ classes on which the debugger is built, available to internal developers and partners, and

a lightweight Python API (available to all users).