Speeding Up zsh Startup with zprof and zsh-defer

The Problem

I noticed my zsh shell was taking several seconds to start up, which was frustrating each time I opened a new terminal. Instead of just accepting the delay, I decided to investigate.

Diagnosing with zmodload zsh/zprof

To find the bottleneck, I used zmodload zsh/zprof at the beginning of my .zshrc file and added zprof at the end to print performance statistics. This showed me which plugins and configurations were causing the slowdown.

I was using the zap plugin manager, which is quite simple, but some of my plugins were taking too long to load. This led me to look for faster alternatives (not blaming zap at all!)

Finding a Solution

My search for better performance led me to sheldon, a blazingly fast plugin manager. But the real game-changer was discovering zsh-defer, which lets you lazy-load plugins.

zsh-defer: The Game Changer

After using sheldon with zsh-defer for a few weeks, I was happy with the speed improvements. However, I wasn’t thrilled about having a separate directory just for sheldon’s configuration. Being the engineer I am, I decided to build my own solution combining the best of both worlds.

My Custom Setup

Here’s my streamlined .zshrc:

source $ZDOTDIR/init.zsh
# Initialize completions with defer
autoload -Uz compinit
if [ "$(date +'%j')" != "$(stat -f '%Sm' -t '%j' ~/.zcompdump 2>/dev/null)" ]; then
    zsh-defer compinit
else
    zsh-defer compinit -C
fi

And the heart of my solution, init.zsh:

PLUGIN_DIR="$HOME/.local/share/zsh/plugins"
PLUGIN_LOCK="$PLUGIN_DIR/.plugins.lock"
[ -d "$PLUGIN_DIR" ] || mkdir -p "$PLUGIN_DIR"

# Reinstall function
update-plugins() {
  rm -fr "$PLUGIN_DIR"
  echo "Plugin lock removed. Restart your shell to reinstall plugins."
}

# Define plugins: "github_repo name"
plugins=(
  "romkatv/zsh-defer"
  "zsh-users/zsh-autosuggestions"
  ...
  "zsh-users/zsh-syntax-highlighting"
)

# Only install plugins if lock file doesn't exist
if [ ! -f "$PLUGIN_LOCK" ]; then
  for plugin in "${plugins[@]}"; do
    plugin_name=${plugin##*/}
    if [ ! -d "$PLUGIN_DIR/$plugin_name" ]; then
      git clone --quiet "https://github.com/$plugin" "$PLUGIN_DIR/$plugin_name" --depth=1
    fi
  done
  date > "$PLUGIN_LOCK"
fi

# Source plugins
source "$PLUGIN_DIR/zsh-defer/zsh-defer.plugin.zsh"
source "$PLUGIN_DIR/zsh-autosuggestions/zsh-autosuggestions.zsh"
...

# Source config files
source "$ZDOTDIR/opts.zsh"
...

# Defer loading
zsh-defer source "$PLUGIN_DIR/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh"
for config in mise.zsh tmux.zsh functions.zsh alias.zsh keymap.zsh path.zsh pnpm.zsh opts.zsh; do
  zsh-defer source "$ZDOTDIR/$config"
done

The Results

After implementing these changes, I ran zprof again to check the performance:

num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)    1           2.83     2.83   30.88%      2.83     2.83   30.88%  autopair-init
 2)    1           1.77     1.77   19.27%      1.77     1.77   19.27%  enable-fzf-tab
 3)    1           1.71     1.71   18.65%      1.71     1.71   18.65%  check_maintenance
 4)    1           0.62     0.62    6.79%      0.62     0.62    6.79%  _history-substring-search-function-callable

The key improvements in my approach:

1. Simple plugin management - No external manager needed, just a basic script that clones plugins
2. Strategic loading - Critical plugins load synchronously, while others are deferred
3. Performance monitoring - Using zprof to validate the improvements
4. Easy maintenance - A simple function to reinstall plugins when needed

My shell now starts almost instantly, and I get all the functionality I need without the wait. The best part is that this solution is lightweight and doesn’t depend on complex plugin managers.