dcmake: a new CMake debugger UI

dcmake: a new CMake debugger UI

April 07, 2026

nullprogram.com/blog/2026/04/07/

CMake has a --debugger mode since 3.27 (July 2023),<br>allowing software to manipulate it interactively through the Debugger<br>Adaptor Protocol (DAP), an HTTP-like protocol passing JSON messages.<br>Debugger front-ends can start, stop, step, breakpoint, query variables,<br>etc. a live CMake. When I came across this mode, I immediately conceived a<br>project putting it to use. Thanks to recent leaps in software engineering<br>productivity, I had a working prototype in 30 minutes, and by the<br>end of that same day, a complete, multi-platform, native, GUI application.<br>I named it dcmake (“debugger for CMake”). I’ve tested it on macOS,<br>Windows, and Linux. Despite only being couple days old, it’s one of the<br>coolest things I’ve ever built. Prior to 2026, I estimate it would have<br>taken me a month to get the tool to this point.

It has a Dear ImGui interface, which I’ve experienced as a user but<br>never built on myself before. Specifically the docking branch. In a<br>sense it’s a toolkit for building debuggers, so it’s playing an enormous<br>role in how quickly I put this project together. All of the “windows” tear<br>out and may be free-floating or docked wherever you like, closely matching<br>the classic Visual Studio UI. I borrowed all the same keybindings: F10 to<br>step over, F11 to step in, F5 to start/continue, shift+F5 to stop. Click<br>on line numbers to toggle breakpoints, right click to run-to-line, hover<br>over variables with the mouse to see their values. Nearly every every UI<br>state persists across sessions, and it opens nearly instantly.

This is just one of many situations I’ve used AI the past month for UI<br>development, and it’s been shockingly effective. I can describe roughly<br>the interface I want, and the AI makes it happen in a matter of minutes.<br>It understands what I mean, filling in the details, sometimes anticipating<br>what I’ll ask for next. If I’m unsure how I want a UI to work, it also<br>offers good advice. If I need simple icons and such, it can draw those,<br>too. It’s all incredibly empowering.

On macOS and Linux it runs on top of GLFW with OpenGL 3 rendering, and on<br>Windows it uses native Win32 windowing and DirectX 11 rendering.

Program arguments given to dcmake populate the top-left arguments text<br>input, which go straight into CMake on start. So you can prepend d to<br>your CMake configuration command to run it inside the debugger. Passing no<br>arguments sets it up for “standard” -B build configuration.

In general, if you don’t have anywhere in particular to look, likely the<br>first thing to do after starting dcmake (in a project) is press F10. It<br>starts CMake paused on the first line of CMakeLists.txt, or whatever<br>script you’re debugging. If you’re trying out dcmake for the first time,<br>that’s a good place to start. Keep pressing F10 to step through that<br>script, watching it run through its configuration. If you F11 through the<br>script then you’ll dive deeper and deeper into CMake itself, which can be<br>insightful.

There is no point in trying to debug --build invocations. It’s just a<br>uniform interface to the underlying build tool, and there is no CMake left<br>to debug at that point. However, it does work with -P script mode<br>invocations. CMake can operate as a platform-agnostic shell script-like<br>tool, but unlike shell scripts you can step through them with a<br>debugger like dcmake.

On Windows it supports Unicode paths all the way through, without a UTF-8<br>manifest. This took some special care, in particular<br>avoiding any C++ standard library I/O functionality. Current frontier AI<br>cannot handle this detail on their own. The macOS platform required a bit<br>of Objective-C, as it often does, and I’m happy I didn’t have to figure<br>that part out myself.

The next release of w64devkit will include dcmake, complementing its<br>recent addition of CMake. This new tool has already proven useful in its<br>own development.

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