Jujutsu (jj) Version Control System

This skill helps you work with Jujutsu, a Git-compatible VCS with mutable commits and automatic rebasing.

Tested with jj v0.37.0 - Commands may differ in other versions.

Important: Automated/Agent Environment

When running as an agent:

1. Always use -m flags to provide messages inline rather than relying on editor prompts:

# Always use -m to avoid editor prompts
jj desc -m "message"      # NOT: jj desc
jj squash -m "message"    # NOT: jj squash (which opens editor)

Editor-based commands will fail in non-interactive environments.

2. Verify operations with jj st after mutations (squash, abandon, rebase, restore) to confirm the operation succeeded.

Core Concepts

The Working Copy is a Commit

In jj, your working directory is always a commit (referenced as @). Changes are automatically snapshotted when you run any jj command. There is no staging area.

There is no need to run jj commit.

Commits Are Mutable

CRITICAL: Unlike git, jj commits can be freely modified after creation. You can update descriptions, squash changes, rebase, and absorb — all without creating new commits. See "Essential Workflow" below for the recommended working pattern.

Change IDs vs Commit IDs

• Change ID: A stable identifier (like tqpwlqmp) that persists when a commit is rewritten — prefer these when referencing commits
• Commit ID: A content hash (like 3ccf7581) that changes when commit content changes

Revsets

jj uses a revset language to select commits in commands. Common revsets:

• @ — the working copy commit
• @- — the parent of the working copy
• ::@ — all ancestors of @
• @:: — all descendants of @
• trunk()..@ — commits between trunk and @ (your branch)
• bookmarks() — all commits with bookmarks

Use revsets with -r flags: jj log -r 'trunk()..@'

Essential Workflow

Starting Work: Describe First, Then Code

Always create your commit message before writing code:

Validate that you're on a blank revision with jj st. If you are not, you should type:

jj new

# First, describe what you intend to do
jj desc -m "Add user authentication to login endpoint"

# Then make your changes - they automatically become part of this commit
# ... edit files ...

# Check status
jj st

Creating Atomic Commits

Each commit should represent ONE logical change. Use this format for commit messages:

Examples:
- "Add validation to user input forms"
- "Fix null pointer in payment processor"
- "Remove deprecated API endpoints"
- "Update dependencies to latest versions"

Viewing History

# View recent commits
jj log

# View with patches
jj log -p

# View specific commit
jj show <change-id>

# View diff of working copy (use --git for familiar +/- format)
jj diff --git

IMPORTANT: jj diff output format: The default jj diff output uses a side-by-side line number format (e.g. 26 26:) that looks very different from git's +/- prefix format. This is normal and correct — it is NOT corrupted or showing stale content. However, to avoid confusion, always use jj diff --git to get standard unified diff format with +/- lines.

Moving Between Commits

# Create a new empty commit on top of current
jj new

# Create new commit with message
jj new -m "Commit message"

# Edit an existing commit (working copy becomes that commit)
jj edit <change-id>

# Edit the previous commit
jj prev -e

# Edit the next commit
jj next -e

Refining Commits

Squashing Changes

Move changes from current commit into its parent:

# Squash all changes into parent
jj squash

Note: jj squash -i opens an interactive UI and will hang in agent environments. Avoid it.

Splitting Commits

Warning: jj split is interactive and will hang in agent environments. To divide a commit, use jj restore to move changes out, then create separate commits manually.

Absorbing Changes

Automatically distribute changes to the commits that last modified those lines:

# Absorb working copy changes into appropriate ancestor commits
jj absorb

Abandoning Commits

Remove a commit entirely (descendants are rebased to its parent):

jj abandon <change-id>

Undoing Operations

Reverse the last jj operation:

jj undo

This reverts the repository to its state before the previous command. Useful for recovering from mistakes like accidental abandon, squash, or rebase.

Rebasing Commits

Move commits to a different parent:

# Rebase current branch onto a destination
jj rebase -d <destination>

# Rebase a specific revision (without descendants) onto a destination
jj rebase -r <change-id> -d <destination>

# Rebase a revision and all its descendants
jj rebase -s <change-id> -d <destination>

# Rebase onto trunk (common: update your branch to latest main)
jj rebase -d main

Restoring Files

Discard changes to specific files or restore files from another revision:

# Discard all uncommitted changes in working copy (restore from parent)
jj restore

# Discard changes to specific files
jj restore path/to/file.txt

# Restore files from a specific revision
jj restore --from <change-id> path/to/file.txt

Working with Bookmarks (Branches)

Bookmarks are jj's equivalent to git branches:

# Create a bookmark at current commit
jj bookmark create my-feature -r@

# Move bookmark to a different commit
jj bookmark move my-feature --to <change-id>

# List bookmarks
jj bookmark list

# Delete a bookmark
jj bookmark delete my-feature

Git Integration

Working with Existing Git Repos

# Clone a git repository
jj git clone <url>

# Initialize jj in an existing git repo
jj git init --colocate

Fetching Remote Changes

# Fetch all branches from the default remote
jj git fetch

# Fetch from a specific remote
jj git fetch --remote <remote-name>

# Fetch specific branches
jj git fetch -b <branch-name>

After fetching, rebase your work onto the updated trunk: jj rebase -d main

Switching Between jj and git (Colocated Repos Only)

This section only applies to colocated repos (where both .jj/ and .git/ exist). In non-colocated repos, do not use git commands — they will corrupt jj state.

In a colocated repository, you can use both jj and git commands with care:

Switching to git mode (e.g., for merge workflows):

# First, ensure your jj working copy is clean
jj st

# Then checkout a branch with git
git checkout <branch-name>

Switching back to jj mode:

# Use jj edit to resume working with jj
jj edit <change-id>

Important notes:

• Git may complain about uncommitted changes if jj's working copy differs from the git HEAD
• ALWAYS ensure your work is committed in jj before switching to git
• After git operations, jj will detect and incorporate the changes on next command

Pushing Changes

When the user asks you to push changes:

# Push a specific bookmark to the remote
jj git push -b <bookmark-name>

# Example: push the main bookmark
jj git push -b main

Before pushing, ensure:

1. Your bookmark points to the correct commit (bookmarks don't auto-advance like git branches)
2. The commits are refined and atomic
3. The user has explicitly requested the push

IMPORTANT: Unlike git branches, jj bookmarks do not automatically move when you create new commits. You must manually update them before pushing:

# Move an existing bookmark to the current commit
jj bookmark move my-feature --to @

# Then push it
jj git push -b my-feature

If no bookmark exists for your changes, create one first:

# Create a bookmark at the current commit
jj bookmark create my-feature

# Then push it
jj git push -b my-feature

Handling Conflicts

jj allows committing conflicts — you can resolve them later:

# View conflicts
jj st

Agent conflict resolution: Do not use jj resolve (interactive). Instead, edit the conflicted files directly to remove conflict markers, then run jj st to verify resolution.

Preserving Commit Quality

IMPORTANT: Because commits are mutable, always refine them before considering work done:

1. Review your commit: jj show @ or jj diff --git
2. Is it atomic? One logical change per commit
3. Is the message clear? Use imperative verb phrase in sentence case format with no full stop: e.g. "Add login endpoint", "Fix null pointer in payment processor", "Remove deprecated API endpoints"
4. Are there unrelated changes? Use jj restore to move changes out, then create separate commits
5. Should changes be elsewhere? Use jj squash or jj absorb

Quick Reference

Best Practices Summary

1. Describe first: Set the commit message before coding
2. One change per commit: Keep commits atomic and focused
3. Use change IDs: They're stable across rewrites
4. Refine commits: Leverage mutability for clean history
5. Embrace the workflow: No staging area, no stashing - just commits