An environment’s contents are declared, not scripted: there is no user Dockerfile. Extra software comes in through mim new and mim modify and is solved together with the language toolchain, so the declaration — not a build log — is what reproduces the environment. The two package sources are covered in Packages:

Python and R libraries that a program needs are not declared here at all: a module’s package.yaml lists them, and mim solves them into the environment when the program is built (Dependencies (py-deps), Dependencies (r-deps), Dependencies (rust-deps)). Pin language versions with --lang (Language toolchains).

Container backends also let you choose the base image with --base: heavy (the default, ubuntu:24.04) or light (debian:bookworm-slim, smaller, fewer preinstalled packages). Both are accepted by new and modify, and changing the base rebuilds the environment.