ADR-006: Zsh as Default Shell

Status: Accepted Date: 2026-02-09 Authors: @sebastienrousseau

Context

Choosing a default shell impacts:

• Developer productivity and workflow
• Plugin ecosystem and extensibility
• Cross-platform compatibility
• Startup performance
• Learning curve for new users

Decision

Use Zsh as the default interactive shell with Zinit as the plugin manager.

Alternatives Considered

Shell	Pros	Cons
Bash	Universal, stable, POSIX	Limited interactive features
Zsh	Rich features, great plugins	Slower than bash (mitigated)
Fish	Modern, user-friendly	Not POSIX, less portable
Nushell	Structured data, modern	Breaking changes, immature

Why Zsh

1. Default on macOS: Pre-installed since Catalina
2. Plugin Ecosystem: Massive library of plugins and themes
3. Compatibility: POSIX-compatible, smooth migration from bash
4. Completion System: Superior tab completion
5. Customization: Highly configurable prompt and behavior
6. Community: Large community, well-documented

Why Zinit

Plugin Manager	Load Time	Features
Oh-My-Zsh	~800ms	Monolithic, many plugins
Prezto	~400ms	Faster, modular
Zinit	~200ms	Turbo mode, fine control
Antibody	~300ms	Simple, fast

Zinit provides:

• Turbo Mode: Deferred loading after prompt
• Ice Modifiers: Fine-grained control over plugin loading
• Binary Installation: Install completions and binaries
• Profiling: Built-in load time profiling

Implementation

Shell Layer System

dot_config/zsh/rc.d/
├── 00-10: Core (env, history, options)
├── 20-49: Middleware (zinit, completions)
├── 50-89: Toolchain (languages, tools)
└── 90-99: UX (prompt, aliases, keybindings)

Zinit Configuration

# Turbo mode: load after prompt displays
zinit ice wait lucid
zinit light zsh-users/zsh-autosuggestions

# Synchronous: needed immediately
zinit light zdharma-continuum/fast-syntax-highlighting

Performance Targets

Metric	Target	Achieved
Cold Start	<500ms	~300ms
Warm Start	<200ms	~150ms
Plugin Load	Async	Yes

Consequences

Positive

• Fast, responsive shell experience
• Rich plugin ecosystem (autosuggestions, syntax highlighting)
• Powerful completion system
• Compatible with existing bash scripts
• Modern prompt with Starship

Negative

• Requires zsh installation on some Linux distros
• Plugin manager adds complexity
• Some bash-isms need adjustment
• Turbo mode can cause brief visual delay

Neutral

• Users can still use bash for scripts
• Configuration more complex than vanilla shell
• Performance monitoring needed

Performance Optimizations

1. Caching: Compile zsh files to .zwc bytecode
2. Lazy Loading: Defer heavy tools (nvm, rvm) until first use
3. Turbo Mode: Load plugins after prompt displays
4. Conditional Loading: Skip unused features

References

• Zsh Documentation
• Zinit Wiki
• Starship Prompt