RTK — Copilot Integration (VS Code Copilot Chat + Copilot CLI)

Usage: Token-optimized CLI proxy (60-90% savings on dev operations)

What's automatic

The .github/copilot-instructions.md file is loaded at session start by both Copilot CLI and VS Code Copilot Chat. It instructs Copilot to prefix commands with rtk automatically.

The .github/hooks/rtk-rewrite.json hook adds a PreToolUse safety net via rtk hook — a cross-platform Rust binary that intercepts raw bash tool calls and rewrites them. No shell scripts, no jq dependency, works on Windows natively.

Meta commands (always use directly)

rtk gain              # Token savings dashboard for this session
rtk gain --history    # Per-command history with savings %
rtk discover          # Scan session history for missed rtk opportunities
rtk proxy <cmd>       # Run raw (no filtering) but still track it

Installation verification

rtk --version   # Should print: rtk X.Y.Z
rtk gain        # Should show a dashboard (not "command not found")
which rtk       # Verify correct binary path

⚠️ Name collision: If rtk gain fails, you may have reachingforthejack/rtk (Rust Type Kit) installed instead. Check which rtk and reinstall from rtk-ai/rtk.

How the hook works

rtk hook reads PreToolUse JSON from stdin, detects the agent format, and responds appropriately:

VS Code Copilot Chat (supports updatedInput — transparent rewrite, no denial):

1. Agent runs git status → rtk hook intercepts via PreToolUse
2. rtk hook detects VS Code format (tool_name/tool_input keys)
3. Returns hookSpecificOutput.updatedInput.command = "rtk git status"
4. Agent runs the rewritten command silently — no denial, no retry

GitHub Copilot CLI (deny-with-suggestion — CLI ignores updatedInput today, see issue #2013):

1. Agent runs git status → rtk hook intercepts via PreToolUse
2. rtk hook detects Copilot CLI format (toolName/toolArgs keys)
3. Returns permissionDecision: deny with reason: "Token savings: use 'rtk git status' instead"
4. Copilot reads the reason and re-runs rtk git status

When Copilot CLI adds updatedInput support, only rtk hook needs updating — no config changes.

Integration comparison

Tool	Mechanism	Hook output	File
Claude Code	PreToolUse hook with updatedInput	Transparent rewrite	hooks/rtk-rewrite.sh
VS Code Copilot Chat	PreToolUse hook with updatedInput	Transparent rewrite	.github/hooks/rtk-rewrite.json
GitHub Copilot CLI	PreToolUse deny-with-suggestion	Denial + retry	.github/hooks/rtk-rewrite.json
OpenCode	Plugin tool.execute.before	Transparent rewrite	hooks/opencode-rtk.ts
(any)	Custom instructions	Prompt-level guidance	.github/copilot-instructions.md