Commits: The Snapshot Mental Model
How Git actually thinks about your project — before any commands
Most Git confusion comes from not having the right mental model. Get this right and every command will make intuitive sense.
Your project is a timeline
Every dot on this line is a commit — a complete snapshot of your project at that moment in time. The arrows show the order. The labels describe what changed.
A commit is not just a diff
It's tempting to think Git saves only what changed between versions. Technically it stores things efficiently, but conceptually a commit is a complete, self-contained snapshot of every file in your project.
Why this matters
Because you can checkout (go to) any commit and see your entire project exactly as it was at that point. Not just the changes — the whole thing.
The commit hash
Every commit gets a unique identifier — a long hexadecimal string like `a1b2c3d4e5f6...`. You'll usually see just the first 7 characters. This hash is how Git identifies every snapshot uniquely, forever.
Example git log output
commit a1b2c3d (HEAD -> main)
Author: You <you@example.com>
Date: Mon Jun 2 14:22:33 2026
Add dark mode toggle
commit e4f5a6b
Author: You <you@example.com>
Date: Sun Jun 1 10:15:07 2026
Fix navigation on mobileWhat HEAD means
HEAD is just a pointer to where you currently are in the timeline. Usually it points to the latest commit on your current branch. When you make a new commit, HEAD advances to it automatically.
Think of HEAD as "you are here"
On a map, there's a dot showing where you are. In Git, HEAD is that dot. It moves forward as you commit, and you can manually move it to look at older snapshots.
What makes a good commit message
Your commit messages are the labels on the timeline. In six months you'll rely on them to understand what happened and why. Good messages are short, specific, and describe what and why — not how.
- Good: "Add user authentication with email/password"
- Good: "Fix mobile menu not closing on outside click"
- Bad: "Updates"
- Bad: "WIP"
- Bad: "asdfg"
Conventional commits (optional but popular)
Many teams prefix messages: feat: for new features, fix: for bug fixes, docs: for documentation, refactor: for code changes that don't add features. Example: "feat: add dark mode toggle"