Language Runtimes

Installs the full runtime lineup — Node, Python, Java, Go, Rust, Ruby on request — under the modern manager set: mise for everything except Python (uv) and Rust (rustup). One manager per runtime; competing managers racing to put shims first in PATH is the top cause of "node is weird" machines.

When NOT to use

• Project-level deps (npm install, venvs, requirements.txt) → native
• pnpm/corepack, databases → web-dev-setup
• JDK specifically for Android Studio/Gradle → mobile-dev-setup
• Upgrading installed runtimes → mac-maintenance

Prerequisites

brew present (→ homebrew-setup).

The rules

1. Detect before installing. [ -d ~/.nvm ], command -v pyenv jenv mise asdf uv fnm volta conda sdk, grep -E 'nvm|pyenv|jenv|mise|asdf|fnm|volta|conda|sdkman' ~/.zshrc ~/.zprofile ~/.zshenv 2>/dev/null, and type -a node python3 java to see what actually wins PATH today.
2. Preserve existing. A working manager stays (an nvm/pyenv/jenv setup is not broken — don't stack mise on top of it for the same runtime). Multiple already present → show the conflict, ask which to keep, disable the loser's init line (with consent), don't delete its data. An explicit user tool choice wins ("install nvm" means nvm — classic-manager details: references/runtime-versions.md).
3. Boundaries: uv owns Python entirely (don't enable mise's python); rustup owns Rust; mise owns node/java/go/ruby.

Safety rails

• .zshrc additions are grep-guarded appends; back up before edits.
• Never sudo pip/npm/gem and never modify system Python/Ruby — macOS's runtimes are part of the OS.
• Disabling a manager = comment/remove its init lines; deleting ~/.nvm, ~/.pyenv etc. only on explicit request (it deletes installed runtimes).

Workflow (fresh machine — the default)

brew install mise uv rustup
grep -q 'mise activate' ~/.zshrc || echo 'eval "$(mise activate zsh)"' >> ~/.zshrc
eval "$(mise activate zsh)"                  # current shell too

# Node - LTS
mise use -g node@lts
# .nvmrc/.node-version support is off by default:
mise settings add idiomatic_version_file_enable_tools node

# Java - Temurin LTS (plain temurin tracks the latest NON-LTS - pin the LTS)
mise use -g java@temurin-25

# Go
mise use -g go@latest

# Ruby (on request; never system Ruby - it's EOL 2.6, immutable)
# mise use -g ruby@3

# Python - uv owns it
uv python install 3.13        # 3.14 is current; 3.13 has the broadest wheel coverage - ask
# Plain `python3` on PATH from uv too? add --default (shims into ~/.local/bin -
# make sure that dir is on PATH):
#   uv python install 3.13 --default
uv tool install ruff          # CLI tools (pipx replacement; installs to ~/.local/bin)
# projects: uv init / uv add / uv run / uv sync

# Rust - rustup (brew formula; NOT brew's `rust`)
export PATH="$(brew --prefix rustup)/bin:$PATH"   # + grep-guarded .zshrc line
rustup default stable

Existing classic setups (nvm / pyenv / jenv)

Preserve-existing wins — keep them running, don't migrate unasked:

• nvm: already sourced from .zshrc; nvm install --lts && nvm alias default 'lts/*' for a new version. Slow-startup mitigation: --no-use on the source line (defers activation; doesn't zero the cost — full lazy-load needs zsh-nvm or switching to mise/fnm).
• pyenv: builds from source — needs brew install openssl readline sqlite3 xz zlib tcl-tk; init lines per its README. uv coexists fine (it can use pyenv's interpreters).
• jenv: jenv add <jdk-home>, jenv versions, jenv global <name>; JDKs from versioned Temurin casks (brew install --cask temurin@25).

Migration to mise/uv only on explicit request: install the modern manager, move the global default over, comment out the old init lines, leave the old data dirs untouched.

Verify

sh "${CLAUDE_SKILL_DIR}/scripts/check.sh"

Fresh shell: node -v (LTS major), python3 --version or uv run python --version, java --version (Temurin LTS), go version, rustc --version — each resolving from its one manager (type -a node shows exactly one manager's path).

Output spec

Done means: every requested runtime installed with exactly one manager active per runtime, global defaults set, init lines present once, fresh-shell verification passes, and any pre-existing setup was preserved or consciously replaced.

Gotchas

• Two managers, one runtime = flaky versions + slow shells. type -a node / which -a python3 expose the race.
• Plain temurin cask / java@latest = newest non-LTS JDK; the LTS is the versioned pin (temurin-25). Multiple JDKs: /usr/libexec/java_home -V.
• uv self update errors on brew installs (standalone-installer feature) — update via brew upgrade uv.
• mise's .nvmrc parsing is opt-in (the idiomatic_version_file setting above); without it, per-project Node pins silently don't apply.
• Node's corepack no longer ships with Node 25+ — pnpm/yarn install changed; that's web-dev-setup territory.
• Homebrew's openjdk formulae are keg-only and need a sudo ln -sfn step before java_home sees them — Temurin casks and mise's java avoid this.
• Facts that age (current LTS lines, versions, classic-manager commands): references/runtime-versions.md.