jj Concepts Guide

JJHub is built natively on Jujutsu (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

jj log --no-graph
# Shows: change_id | commit_id | description

jj calls branches “bookmarks”. They work similarly to git branches:

jj bookmark create feature/my-feature
jj bookmark set main -r @

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

# Edit a file, then describe what you did:
jj describe -m "Add feature X"

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

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

# Create a stack
jj new main -m "Feature base"
jj new -m "Feature detail"

# Push the whole stack
jj git push --all

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

jjhub land create --title "Add feature X"

jj tracks all operations (not just commits):

jj op log  # View operation history
jj undo    # Undo the last operation