rtk filters and compresses command outputs before they reach your LLM context. Single Rust binary, 100+ supported commands, <10ms overhead.
What RTK Does
RTK intercepts shell commands and compresses their output before your agent reads it.
Operation
What RTK does to the output
ls / tree
Tree format with file counts instead of one line per entry
cat / read
Smart file reading: signatures and structure over full bodies
grep / rg
Truncates long lines, groups matches by file
ast-grep
Groups structural matches by file, caps overflow
git status
Compact stat format, grouped by state
git diff
Reduced context, headers stripped
git log
Hash, author and subject only
git add/commit/push
Confirmation line instead of full progress output
cargo test / npm test
Failures only, passing tests collapsed to a count
ruff check
Grouped by rule and file
sqlfluff lint
Grouped by rule and file
pytest
Failures only, traceback trimmed
go test
NDJSON parsed, failures only
docker ps
Essential fields only
How Savings Work
RTK reduces the bash output your agent reads. That is what RTK measures, and it is not the same as cutting your bill by the same amount.
Bash output is one contributor to input tokens, alongside your prompt, the system prompt and conversation history. Input tokens are in turn only part of the bill, which also counts output tokens. The reduction dilutes at every step.
The token counts RTK reports are estimated as bytes / 4 — RTK ships no tokenizer, so the percentages are reliable but the absolute token numbers are approximate.
brew install rtk # macOS / Linux
winget install rtk-ai.rtk # Windows
curl -fsSL https://raw.githubusercontent.com/rtk-ai/rtk/refs/heads/master/install.sh | sh
Then check you have the right package — another project named "rtk" exists on crates.io:
rtk --version # any current version
rtk gain # must show the savings dashboard, not "command not found"
Cargo, pre-built binaries, native Windows, WSL, and uninstall: Installation guide
What You Install
RTK ships as three downloads. The two rtk editions install a binary with the same name — hooks, scripts and agent config work unchanged across both — so they cannot be installed together. Uninstall one before installing the other.
flowchart TD
agent["Your coding agent"]
subgraph editions["Pick one · both install a binary named rtk"]
direction LR
full["<b>rtk</b><br/>Apache-2.0 + BUSL-1.1<br/>hooks · filters · engine"]
oss["<b>rtk-oss</b><br/>Apache-2.0 only<br/>hooks · filters"]
end
proxy["<b>rtk-proxy</b><br/>BUSL-1.1<br/>compresses API traffic"]
agent -->|"command output"| full
agent -->|"command output"| oss
agent -.->|"API traffic"| proxy
classDef apache stroke:#2da44e,stroke-width:2px,fill:none
classDef busl stroke:#0969da,stroke-width:2px,fill:none
classDef mixed stroke:#8250df,stroke-width:2px,fill:none
classDef plain stroke:#8c959f,stroke-width:1px,fill:none
class full mixed
class oss apache
class proxy busl
class agent plain
style editions fill:none,stroke:#d0d7de,stroke-dasharray:4 4
Download
Licence
Contains
rtk-<target>
Apache-2.0 + BUSL-1.1
Hook core, every command filter, and the compression engine
rtk-oss-<target>
Apache-2.0 only
Hook core and every command filter. No engine.
rtk-proxy-<target>
BUSL-1.1
The RTK Proxy daemon. Never bundled with either rtk.
Production use is free, engine and daemon included. What the BUSL grant does not cover is offering RTK or a derivative to third parties as a commercial product or service — for that, contact [email protected].
What the Apache-2.0 edition omits and where the licence boundary falls: Editions and Licensing
Quick Start
# 1. Install for your AI tool
rtk init -g # Claude Code / Copilot (default)
rtk init -g --gemini # Gemini CLI
rtk init -g --codex # Codex (OpenAI)
rtk init -g --agent cursor # Cursor
rtk init -g --agent windsurf # Windsurf
rtk init --agent cline # Cline / Roo Code
rtk init --agent kilocode # Kilo Code
rtk init --agent antigravity # Google Antigravity
rtk init --agent kimi # Kimi AI
rtk init -g --agent pi # Pi
rtk init --agent omp # Oh My Pi (OMP)
rtk init --agent hermes # Hermes
rtk init -g --agent droid # Factory Droid
rtk init --agent trae # Trae (project: .trae/hooks.json)
rtk init -g --agent trae # Trae global: ~/.trae and existing ~/.trae-cn# 2. Restart your AI tool, then test
git status # Automatically rewritten to rtk git status
The agent receives compact output without ever calling rtk explicitly.
The hook only fires on Bash tool calls. Built-in tools like Read, Grep and Glob do not pass through it. Use shell commands (cat, rg, find) or call rtk read, rtk grep, rtk find directly.
Deduplication - Collapses repeated log lines with counts
Does RTK break Claude's prompt cache? No. RTK filters output once per command. The result is stored in history and cached normally on subsequent API calls, so the cache keeps working as expected. Smaller outputs also mean cheaper cache writes and reads. See Troubleshooting for details.
Supported AI Tools
RTK supports 18 AI coding tools. Each integration rewrites shell commands to rtk equivalents, reducing the bash output the agent reads where the agent supports command interception.
Tool
Install
Method
Claude Code
rtk init -g
PreToolUse hook (native binary)
GitHub Copilot (VS Code)
rtk init -g --copilot
PreToolUse hook — transparent rewrite
GitHub Copilot CLI
rtk init -g --copilot
PreToolUse deny-with-suggestion (CLI limitation)
Cursor
rtk init -g --agent cursor
preToolUse hook (hooks.json)
Gemini CLI
rtk init -g --gemini
BeforeTool hook
Codex
rtk init -g --codex
PreToolUse hook (updatedInput) + AGENTS.md
Windsurf
rtk init -g --agent windsurf
.windsurfrules (project-scoped)
Cline / Roo Code
rtk init --agent cline
.clinerules (project-scoped)
OpenCode
rtk init -g --opencode
Plugin TS (execute.before / tool.execute.before), needs 1.18.29 or newer
.agents/plugins/rtk/ (project) or ~/.gemini/config/plugins/rtk/ (global): plugin.json, hooks.json, rules/AGENTS.md
Kimi AI
rtk init --agent kimi
AGENTS.md (project-scoped)
Factory Droid
rtk init -g --agent droid (or per-project)
PreToolUse hook in ~/.factory/hooks.json (matcher Execute)
Trae
rtk init --agent trae
Native PreToolUse hook in .trae/hooks.json (RunCommand)
Trae (global)
rtk init -g --agent trae
~/.trae/hooks.json, plus ~/.trae-cn/hooks.json when that directory exists
For per-agent setup details, override controls, and graceful degradation, see the Supported Agents guide. The Hermes plugin source and tests live in hooks/hermes/; installed Hermes runtime files still live under ~/.hermes/plugins/rtk-rewrite/.
What RTK Covers
100+ commands across Git, GitHub CLI, Cargo/Rust, JavaScript (npm, pnpm, vitest, jest, tsc, Next.js, Playwright, Prisma), Python (ruff, pytest, mypy, pip), Go (go test, golangci-lint), Ruby, .NET, JVM (Gradle, Maven), PHP, Docker, Kubernetes, AWS, Terraform, and the file/search builtins.
-v, --verbose # increase verbosity (-v, -vv, -vvv)
rtk bypass <cmd> # run one command unfiltered, still tracked
rtk optimizes command output before your agent reads it. The rtk-proxy daemon extends the same engine to your agent's provider-API traffic — a local background process that sits between your agent and the provider and runs the pipeline on the traffic itself: it compresses payloads, strips bytes no model ever needed before forwarding, and carries the calls your pipeline routes to cheaper models, so they borrow the credential your agent already sends and show up in rtk gain. It can also align prompt-cache breakpoints where the agent leaves them open (opt-in).
rtk claude # start the daemon if needed, then launch Claude through it
rtk llm-proxy status # is it up
rtk gain # savings, command-filtering and proxy side by side
Two independent ways in, because not every harness has a session hook:
What it does
rtk init -g
Offers to set it up once: writes the base URL and the rtk:proxy pipeline, then asks how the daemon should come back after a reboot — SessionStart hook, background service, or neither.
rtk <harness>
No configuration at all. Starts the daemon, points the harness at it, then execs it. Needs no hook system, which is why it covers harnesses that have none.
rtk <harness> resolving is itself the signal that traffic really goes through the daemon — the subcommand exists only where redirection is verified. Today that is rtk claude. A harness without one is never silently unproxied: it falls through to plain passthrough, and rtk llm-proxy setup lists what can be launched.
It is a separate binary under a separate licence (BUSL-1.1), shipped as its own rtk-proxy-<target> archive — rtk never links it.
Everything RTK does — which commands get rewritten, what happens to a tool's output, what the proxy compresses — is expressed in one composable file. The engine (engine/, crate rtk-engine, BUSL-1.1) reads it, so the levers are configurable instead of hard-coded.
Upgrading changes nothing. With no pipeline file you are on rtk:default: the same PreToolUse rewrite, the same awareness file, your filters.toml, your config.toml. Everything beyond that is opt-in, one line at a time:
RTK collects no command content and no file contents. Telemetry is anonymous and off by default — it sends nothing until you opt in with explicit consent (GDPR Art. 6 & 7) via rtk telemetry enable, and documented in Telemetry & Privacy.
It links one component under a different licence. rtk-engine (engine/) is
BUSL-1.1, source-available: see engine/LICENSE. Its
Additional Use Grant permits production use as part of the rtk binary, so
running rtk is covered; using the engine on its own, or inside another
product, is not until the Change Date.
The rtk-proxy daemon (proxy/) is BUSL-1.1 on the same terms and ships as
its own archive with its licence alongside — rtk never links it.
