RTK (Rust Token Killer)

A small CLI that sits between Claude and the shell and trims command output before it reaches the context window. git status, grep, test runs, ls, gh and friends come back grouped, deduplicated and truncated. Source: rtk-ai/rtk (Apache 2.0).

brew install rtk          # or: cargo install rtk
rtk init --global         # wires the Claude Code hook and drops an RTK.md into ~/.claude

How it fires

rtk init --global adds one PreToolUse hook on Bash that runs rtk hook claude. The hook rewrites a known command to its rtk equivalent (grep becomes rtk grep, git log becomes rtk git log) before it runs. Nothing changes in how you or the model type commands. Commands it does not know pass through untouched.

The global RTK.md it installs is four lines, @-imported from CLAUDE.md, so the model knows the three commands that are never rewritten:

Command	What it is for
`rtk gain`	Savings so far, overall and per command
`rtk discover`	Commands you ran that RTK could have filtered but did not
`rtk proxy <cmd>`	Run a command raw, no filtering. Use it when you are debugging and need every byte

What it saves

On the author’s machine after roughly 240,000 commands: 1.33 billion tokens saved, 80.8% of the output that would otherwise have entered context. rtk grep alone accounts for about half.

rtk gain               # your own numbers
rtk cc-economics       # spend (via ccusage) against what RTK saved

Where it bites

Truncation hides the line you wanted. rtk grep caps line length and result count. When a search seems to miss something, re-run it with rtk proxy grep ... before concluding it is not there.
Flags it does not understand. Some native flags are dropped with a warning (rtk find ignores -prune, for example). The warning is on stderr; read it.
Name collision. There is an unrelated Rust crate also called rtk. If rtk gain is “command not found”, you installed the wrong one.
Hooks that parse output. Your own hooks see the filtered output too. A hook that greps test output for a pass count should call the underlying tool via rtk proxy.

Turning it off

Remove the rtk hook claude entry from settings.json, or prefix single commands with rtk proxy. Uninstalling the binary without removing the hook will break every Bash call.