How I Optimized My Zsh Startup Time

Mon, 11 May 2026 00:00:00 +0000

My zsh prompt was taking close to a second on a fresh terminal. Not catastrophic, but you feel it every time tmux spawns a new pane, which for me is constantly. The config had been growing for years and nobody had been auditing it.

What follows is the audit, and the eight things I changed.

Measure first

# Cold-start benchmark (run a few times, watch the variance):
for i in {1..5}; do time zsh -i -c exit; done

# In-shell flamegraph:
# 1. Uncomment `zmodload zsh/zprof` at the top of .zshrc
# 2. Add `zprof` at the bottom
# 3. Open a new shell
zprof | head -40

zprof is the one that helped most. It prints which function calls and evals are burning time, sorted by self-time and call count.

Shell on Saurabh Kumar

How I Optimized My Zsh Startup Time

Measure first