Janus is open source, which means the whole source code is available for both its core internals and all plugins. As such, it's easy to write code to fix issues, add new features, implement new modules and so on.

You don't really need any integrated development environment (IDE) to write code for Janus, but in case you do want to make use of one, you may need to tweak your development environment accordingly. The Janus codebase makes use of many macros defined at configure time to figure out what's available and what should be compiled, for instance, and the IDE you're using may need to be aware of those to do its job.

The following snippet is an example of how you can configure, for instance, Visual Studio Code on Ubuntu 20.04:

{
    "configurations": [
        {
            "name": "Linux",
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "gnu11",
            "cppStandard": "gnu++17",
            "includePath": [
                "${workspaceFolder}/**",
                "/usr/lib/x86_64-linux-gnu/glib-2.0/include",
                "/usr/include/glib-2.0",
                "/usr/include/nice",
                "/usr/include/sofia-sip-1.12"
            ],
            "intelliSenseMode": "linux-gcc-x64",
            "systemIncludePath": [
                "/usr/lib/gcc/x86_64-linux-gnu/9/include",
                "/usr/local/include",
                "/usr/include/x86_64-linux-gnu",
                "/usr/include"
            ],
            "defines": [
                "CONFDIR=\"\"",
                "EVENTDIR=\"\"",
                "HAVE_CLOSE_ASYNC=1",
                "HAS_DTLS_WINDOW_SIZE=1",
                "HAVE_ICE_NOMINATION=1",
                "HAVE_LIBCURL=1",
                "HAVE_LIBNICE_TCP=1",
                "HAVE_LIBOGG=1",
                "HAVE_LIBOPUS=1",
                "HAVE_LIBWEBSOCKETS_PEER_SIMPLE=1",
                "HAVE_PORTRANGE=1",
                "HAVE_SCTP=1",
                "HAVE_SRTP_2=1",
                "LOGGERDIR=\"\"",
                "PLUGINDIR=\"\"",
                "TRANSPORTDIR=\"\""
            ]
        }
    ],
    "version": 4
}