Gym: Skill for Claude Code

gh-stack

gh stack is a GitHub CLI extension for managing stacked branches and pull requests. A stack is an ordered list of branches where each branch builds on the one below it, rooted on a trunk branch (typically the repo's default branch). Each branch maps to one PR whose base is the branch below it, so reviewers see only the diff for that layer.

main (trunk)
 └── feat/auth-layer     → PR #1 (base: main)               - bottom (closest to trunk)
  └── feat/api-endpoints → PR #2 (base: feat/auth-layer)
   └── feat/frontend     → PR #3 (base: feat/api-endpoints) - top (furthest from trunk)

The bottom of the stack is the branch closest to the trunk, and the top is the branch furthest from the trunk. Each branch inherits from the one below it. Navigation commands (up, down, top, bottom) follow this model: up moves away from trunk, down moves toward it.

When to use this skill

Use this skill when the user wants to:

• Break a large change into a chain of small, reviewable PRs
• Create, rebase, push, or sync a stack of dependent branches
• Navigate between layers of a branch stack
• View the status of stacked PRs
• Tear down and rebuild a stack to remove, reorder, or rename branches

Prerequisites

The GitHub CLI (gh) v2.0+ must be installed and authenticated. Install the extension with:

gh extension install github/gh-stack

Before using gh stack, configure git to prevent interactive prompts:

git config rerere.enabled true           # remember conflict resolutions (skips prompt on init)
git config remote.pushDefault origin     # if multiple remotes exist (skips remote picker)

Agent rules

All gh stack commands must be run non-interactively. Every command invocation must include the flags and positional arguments needed to avoid prompts, TUIs, and interactive menus. If a command would prompt for input, it will hang indefinitely.

1. Always supply branch names as positional arguments to init, add, and checkout. Running these commands without arguments triggers interactive prompts.
2. When a prefix is set, pass only the suffix to add. gh stack add auth with prefix feat → feat/auth. Passing feat/auth creates feat/feat/auth.
3. Always use --auto with gh stack submit to auto-generate PR titles. Without --auto, submit prompts for a title for each new PR.
4. Always use --json with gh stack view. Without --json, the command launches an interactive TUI that cannot be operated by agents. There is no other appropriate flag — always pass --json.
5. Use --remote <name> when multiple remotes are configured, or pre-configure git config remote.pushDefault origin. Without this, push, submit, sync, link, and checkout trigger an interactive remote picker.
6. Avoid branches shared across multiple stacks. If a branch belongs to multiple stacks, commands exit with code 6. Check out a non-shared branch first.
7. Plan your stack layers by dependency order before writing code. Foundational changes (models, APIs, shared utilities) go in lower branches; dependent changes (UI, consumers) go in higher branches. Think through the dependency chain before running gh stack init.
8. Use standard git add and git commit for staging and committing. This gives you full control over which changes go into each branch. The -Am shortcut is available but should not be the default approach—stacked PRs are most effective when each branch contains a deliberate, logical set of changes.
9. Navigate down the stack when you need to change a lower layer. If you're working on a frontend branch and realize you need API changes, don't hack around it at the current layer. Navigate to the appropriate branch (gh stack down, gh stack checkout, or gh stack bottom), make and commit the changes there, run gh stack rebase --upstack, then navigate back up to continue.
10. Use gh stack link for external tool workflows. When branches are managed by an external tool (jj, Sapling, etc.), use gh stack link branch-a branch-b. link does not rely on local tracking state and is intended for API-driven PR and stack management. Always provide at least 2 branch names or PR numbers.