> ## Documentation Index
> Fetch the complete documentation index at: https://docs.jjhub.tech/llms.txt
> Use this file to discover all available pages before exploring further.

# jj Concepts Guide

> Understanding Jujutsu (jj) concepts as used by JJHub

# jj Concepts Guide

JJHub is built natively on [Jujutsu (jj)](https://github.com/jj-vcs/jj), a next-generation VCS. This guide explains key jj concepts.

## Changes vs. Commits

In jj, a **change** is the fundamental unit of work. Unlike git commits:

* Changes have a **stable Change ID** (e.g., `qzknlmop`) that doesn't change when you amend
* The commit hash changes on amend, but the Change ID persists
* JJHub tracks and displays Change IDs everywhere

```bash theme={null}
jj log --no-graph
# Shows: change_id | commit_id | description
```

## Bookmarks (not Branches)

jj calls branches "bookmarks". They work similarly to git branches:

```bash theme={null}
jj bookmark create feature/my-feature
jj bookmark set main -r @
```

## The Working Copy

jj treats the working directory as an uncommitted change. You don't need `git add` - changes are automatically included in the current change:

```bash theme={null}
# Edit a file, then describe what you did:
jj describe -m "Add feature X"
```

## Stacked Changes

JJHub's premiere feature is first-class support for stacked changes:

```
main
  └── feature-base
        └── feature-detail (current)
```

```bash theme={null}
# Create a stack
jj new main -m "Feature base"
jj new -m "Feature detail"

# Push the whole stack
jj git push --all
```

## Landing Requests (not Pull Requests)

JJHub uses "Landing Requests" (LRs) instead of "Pull Requests". LRs natively understand stacked changes and Change IDs.

```bash theme={null}
jjhub land create --title "Add feature X"
```

## Operation Log

jj tracks all operations (not just commits):

```bash theme={null}
jj op log  # View operation history
jj undo    # Undo the last operation
```

## Key Differences from Git

| Concept         | git                  | jj                         |
| --------------- | -------------------- | -------------------------- |
| Working state   | Staging area         | Working copy change        |
| Stable ID       | Branch name          | Change ID                  |
| Branch          | Branch               | Bookmark                   |
| Amend           | `git commit --amend` | `jj describe` + auto-amend |
| History rewrite | Rebasing required    | First-class, safe          |