PascalsLetter is EquityBot's distribution of RTK, the Rust Token Killer. RTK filters and compresses command output before it reaches your coding agent's context: one Rust binary, more than 100 supported commands. PascalsLetter tracks upstream RTK and adds fixes where compression lost or mangled output an agent needed, several of them on Windows. It installs a binary named rtk, so hooks, agent configuration and every rtk command work unchanged.
PascalsLetter has no prebuilt binaries. Build it from source with Rust:
cargo install --git https://github.com/EquityBot/PascalsLetter rtk --locked
rtk --version # rtk 1.0.1+pascalsletterPascalsLetter and upstream RTK both install rtk, so uninstall any Homebrew, winget or install.sh copy of RTK first. Add --no-default-features for the Apache-2.0-only build without the compression engine. Then set up your agent with rtk init as in Quick Start. The rtk-proxy daemon is a separate package that this command does not install; build it with cargo build --release --manifest-path proxy/Cargo.toml.
Each change has a regression test, except grep_max_results.
| Area | Change |
|---|---|
| Windows arguments | Arguments passed through MSYS keep their exact text: #\[ignore, *.rs, {a,b}, ~ and don't are no longer rewritten (rtk-ai/rtk#4737). |
rtk rg on Windows |
A pathless rtk rg foo with no piped or redirected stdin keeps every filename, following ripgrep's own stdin rule. |
grep and rg |
Output is capped only when that saves at least a third or is the only form under [limits] agent_output_max_chars. Long lines are clipped around the match, located in the engine's own pattern dialect. grep_max_results is honoured, and a partial [limits] table no longer drops the whole config. |
git diff |
Shown verbatim up to agent_output_max_chars. Above it, a compacted diff or show ends with [full output: rtk recall <hash>], or [full diff: rtk git diff --no-compact] when recall cannot store it. |
rtk read |
Exact line ranges, and a missing-file error worded as cat words it. |
gh api |
GitHub API *_url links are dropped, with the whole response kept for rtk recall. Anything left unfiltered is written back byte for byte, and --jq and --template are untouched. |
yadm |
Removed from the git rewrite rule, which would run git on the current project instead of yadm's dotfiles repository. It goes through rtk yadm, and rtk discover lists it as unhandled, as it does jq and other commands with only a TOML filter. From kylehgc/rtk by RawNuke (Apache-2.0); see rtk-ai/rtk#3408. |
rtk gain |
The summary, per-command and daily, weekly and monthly tables count an oversised row at a fixed 7,500-token cap, and the headline figure is net. |
Generally useful fixes are offered upstream as draft pull requests, listed in FORKS.md.
Everything below describes RTK as PascalsLetter inherits it. Guide links go to this repository's copy of the RTK guide; its install commands install upstream RTK, not PascalsLetter.
rtk filters and compresses command outputs before they reach your LLM context. Single Rust binary, 100+ supported commands, <10ms overhead.
Angular builds are supported with rtk ng build: compact build tables with every bundle and diagnostic retained.
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 |
Verbatim up to the output cap; above it, a stat summary and 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 |
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.
Full explanation: How RTK Savings Work
# 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 statusThe 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.
Per-agent setup,
--dry-run, and uninstall: Quick Start · Supported Agents
Without rtk: With rtk:
Claude --git status--> shell --> git Claude --git status--> RTK --> git
^ | ^ | |
| full raw output | | compact output | filter |
+-----------------------------------+ +------- (filtered) ---+----------+
Four strategies applied per command type:
- Smart Filtering - Removes noise (comments, whitespace, boilerplate)
- Grouping - Aggregates similar items (files by directory, errors by type)
- Truncation - Keeps relevant context, cuts redundancy
- 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.
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 |
| OpenClaw | openclaw plugins install ./openclaw |
Plugin TS (before_tool_call) |
| Pi | rtk init -g --agent pi (global) |
TypeScript extension (tool_call) |
| Oh My Pi (OMP) | rtk init -g --agent omp (global) / rtk init --agent omp (project) |
TypeScript extension (tool_call, shared with Pi) |
| Hermes | rtk init --agent hermes |
Python plugin adapter (terminal command mutation via rtk rewrite) |
| Mistral Vibe | rtk init -g --agent vibe |
pre_tool hook (hooks.toml) |
| Kilo Code | rtk init --agent kilocode |
.kilocode/rules/rtk-rules.md (project-scoped) |
| Google Antigravity | rtk init --agent antigravity / rtk init -g --agent antigravity |
.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/.
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 trackedEvery command and its filter: What RTK Optimizes
rtk gain # Summary stats
rtk gain --graph # ASCII graph (last 30 days)
rtk gain --history # Recent command history
rtk gain --daily # Day-by-day breakdown
rtk gain --all --format json # JSON export for dashboards
rtk discover # Find missed savings opportunities
rtk discover --all --since 7 # All projects, last 7 days
rtk session # Show RTK adoption across recent sessionsAttribution, the live dashboard and export formats: Token Savings Analytics
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 sideTwo 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.
Setup and subcommands: RTK Proxy · what it compresses: What the Proxy Compresses · settings and endpoints: Proxy Configuration
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:
# ~/.config/rtk/pipeline.toml
[pipeline]
extends = ["rtk:posthook", "rtk:proxy"]The tour: Pipelines · the reference: Writing a Pipeline, Conditions and Judges, Methods, Tasks and Upstreams · the commands: Pipeline Commands · write your own method: Plugins
The full user guide starts at docs/guide.
| Installation | every install method, Windows, WSL, uninstall |
| Quick Start | per-agent init, --dry-run, first savings |
| Supported Agents | setup detail, override controls, degradation |
| Agent Coverage | what each agent's hook API lets RTK do |
| What RTK Optimizes | every command and its filter |
| Configuration | config.toml, env vars, recall recovery |
| Token Savings Analytics | rtk gain in full |
| Pipelines | the engine: pipeline.toml, rules, judges, tasks, sharing |
| RTK Proxy | the daemon: setup, what it compresses, settings |
| Editions and Licensing | what each download contains |
| Telemetry & Privacy | what is collected, how to opt in, your GDPR rights |
| Troubleshooting | common issues, prompt-cache questions |
Repository references: engine/README.md · proxy/README.md · ARCHITECTURE.md · CONTRIBUTING.md · SECURITY.md
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.
PascalsLetter is built on RTK by rtk-ai, founded by Patrick Szymkowiak, with core contributors Florian Bruniaux, Adrien Eppling, Nicolas Le Cam and Takayuki Maeda. Translations of the upstream README: Français, 中文, 日本語, 한국어, Español and Português.
The banner's lettering and emblem are drawn from Cascadia Mono glyphs (SIL OFL 1.1).
Report PascalsLetter problems in this repository's issues. For RTK itself, use rtk-ai/rtk or its Discord.
The rtk CLI is Apache-2.0: see LICENSE.
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.
Editions and Licensing sets out what the Apache-2.0-only build omits and where the BUSL-1.1 grant stops. See also DISCLAIMER.md.
Congratulations, you've just advanced a Compression level.
Made by EquityBot. Ad gloriam eius, non meam.