bootprint docker capture IMAGE and bootprint docker diagnose IMAGE --against SNAPSHOT inspect an image already present locally. Bootprint never pulls an absent image.
The temporary container uses --rm, --read-only, --network none, and a fixed Ruby inspection script. No port is required. The container reports Ruby/gem/platform data, native libraries, installed dpkg/apk package names when available, working-directory permissions, and image entrypoint/command metadata.
The image must contain a working ruby executable. Docker errors are returned as exit code 4 with sanitized stderr. Bootprint never lists or inspects unrelated running containers.