ztk is a CLI proxy that reduces LLM token consumption by intercepting and compressing shell command output. It sits between AI agents (Claude Code, Cursor, Gemini CLI) and the shell, executing commands normally but returning filtered output through a six-stage pipeline. The tool removes noise like diff metadata, test runner verbosity, and redundant directory listings while preserving essential information such as error messages and exit codes. Built in Zig with zero dependencies, it features a Thompson NFA regex engine for runtime filters, SIMD-accelerated text processing, and an mmap'd session cache to avoid repeated output for unchanged commands.