jj-undo

Undo the last operation

$ jj undo

jj undo [OPTIONS]

--at
    Undo operations up to and including the operation that introduced the specified REVISION. This allows for more precise control over which operations are reverted, rather than just the very last one. The REVISION can be an operation ID or a commit ID associated with an operation.

--dry-run
    Show what operations would be undone and what the resulting repository state would be, without actually performing the undo operation. This is useful for previewing the impact of jj-undo before committing to it.

-h, --help
    Display a help message and exit.

jj-undo is a powerful command within the Jujutsu (jj) version control system that allows users to easily reverse the effects of their previous jj operations. Unlike traditional VCS systems that might focus on reverting file changes, jj-undo operates on the repository's operation log.

Every command that modifies the repository's state—such as jj commit, jj rebase, jj branch create, or even jj restore—records an entry in this log. jj-undo effectively steps back one or more entries in this log, restoring the repository to the state it was in before the undone operations. This provides a robust safety net, making it simple to recover from accidental or incorrect commands without complex manual intervention. It's especially useful for exploratory workflows where frequent command usage might lead to unexpected or undesirable repository states, allowing developers to experiment confidently.

jj-undo only reverses jj operations; it does not revert external file changes or modifications made outside of the jj command line.

While powerful, using jj-undo with the --at option requires a good understanding of the operation log to ensure the correct operations are targeted. Care should also be exercised when undoing operations that have already been shared or pushed, as this can create divergent history for collaborators if not handled carefully with subsequent operations like jj move or jj squash.

jj-undo fundamentally relies on Jujutsu's internal operation log. Every single command that modifies the repository's state, from creating new commits to rebasing or amending existing ones, records a unique entry in this log. jj-undo navigates this log backwards, effectively rewinding the repository to a previous state. Users can inspect this chronological record of operations using the jj op log command to understand the history of their repository's transformations.

This command is particularly invaluable in exploratory development and rapid prototyping. Developers can experiment freely with various jj commands—testing different rebase strategies, creating speculative branches, or rewriting history—without the fear of irrevocably corrupting their repository state. If an operation doesn't yield the desired result, jj-undo provides an immediate and reliable way to revert to a known good state, thereby fostering more confident experimentation and reducing cognitive load.

Jujutsu (jj) emerged as a modern, experimental version control system designed to address some of the complexities and limitations of Git. Developed primarily by Martin von Gagern at Google, jj began its journey around 2020-2021. The jj-undo command is a foundational component of jj's design philosophy, emphasizing an easily navigable and reversible history. It was integrated from early versions, leveraging the robust operation log as a core mechanism for repository state management. This 'infinite undo' capability aims to make complex VCS operations feel inherently safer and more intuitive, significantly enhancing the developer experience by reducing fear of making irreversible mistakes.

jj op log(1), jj op restore(1), jj log(1), git revert(1)