Dive

Dive is a tool for inspecting Docker images layer by layer. It's a terminal UI that lets you browse every file in every layer of a Docker image, see what was added/modified/removed, and spot wasted space.

MIT license, written in Go. Run `dive your-image:tag` and get an interactive view: layers on the left, filesystem on the right. It highlights files that exist in one layer but get deleted in a later one (wasted space). Shows you the efficiency score of your image. Works in CI too. Set a threshold and fail the build if the image is too bloated.

Fully free. Single binary, no paid tier, no service component. Every developer who builds Docker images should have this installed. The insight is immediate. You'll find multi-megabyte temp files, package manager caches, and build artifacts sitting in intermediate layers that you thought your `RUN rm` cleaned up (it didn't; each layer is immutable).

The catch: Dive shows you the problem but doesn't fix it. You still need to restructure your Dockerfile: multi-stage builds, combined RUN commands, a proper .dockerignore. And the TUI can be slow on very large images (5GB+). But for diagnosing bloat, nothing else comes close.