slowrc

Why does your terminal take so long to open?
slowrc times your shell's startup, shows exactly which lines of your .zshrc / .bashrc cost the most, and fixes the slow ones safely.

uvx slowrc          # see where the time goes
uvx slowrc --fix    # fix it

_{Demo run on a sandboxed home directory with a typical setup: nvm, pyenv, Homebrew, kubectl completions.}

How it works

1. Times your real startup a few times (median).

2. Traces one startup with the shell's own tracing (timestamps on every line it runs), then charges each line's time to the line in your file that caused it. For example, 250 ms deep inside nvm.sh shows up as ~/.zshrc:3. Tracing overhead is measured and subtracted.

3. Recognises the usual suspects and how to fix each one.

4. With --fix: backs up your files, applies the fixes, then starts a fresh shell and checks it behaves exactly the same:

   • it still starts cleanly
   • nothing went missing from PATH
   • node resolves to the same binary
   • no new errors appear

   If anything differs, every file is restored automatically.

What it fixes

It also points out what it won't touch automatically: conda's base environment, oh-my-zsh plugin weight, SDKMAN!, RVM, a global compinit in /etc/zsh/zshrc, and any other line over 50 ms.

Only init commands whose output never changes between sessions get cached. Things like ssh-agent, keychain or fnm env are left alone.

Safety

• Nothing is changed without --fix. The report alone is read-only.
• Every edited file gets a timestamped backup next to it, and slowrc --undo restores them byte for byte.
• Each change is marked with a # slowrc: comment saying what the line used to be.
• System files (/etc/...) are never edited.

Options

slowrc --shell bash          # default: your $SHELL
slowrc --login / --no-login  # default: login on macOS, interactive on Linux (what terminals use)
slowrc --runs 20             # more timing runs
slowrc --json                # machine-readable report

zsh and bash on macOS and Linux. Line-by-line profiling of bash needs bash 5+ (macOS ships 3.2: brew install bash). If something in your startup files waits for input (like tmux auto-attach), it can skip itself when $SLOWRC is set.

License

MIT