hax

A minimalist, terminal-native coding agent written in C.

Key features

• Lightweight by design — A single native C binary with a small dependency set. Starts instantly, and uses very small amount of memory (just a few MBs) - so more RAM is left for your local LLMs.
• Local models are first-class — Start llama-server -m [model].gguf, then hax --provider llama.cpp, and hax auto-discovers the model and runtime capabilities. No custom provider config block needed for the default setup.
• Respects your terminal — Streaming Markdown and live tool output, reflowed for display in the terminal. Only redraws the current streaming line or the input area, native scrollback is preserved. Does not take over or mess with your terminal.
• Inspectable — See exactly what was sent to the model and what it replied in a usable transcript view (Ctrl+T). Optionally collect a detailed wire protocol trace.
• Use any provider/model — Supports OpenAI (+compatible), Anthropic (+compatible), Codex (via ChatGPT subscription), OpenRouter, llama.cpp, etc.
• Well-behaved Unix tool — XDG paths, clean stdout in -p one-shot mode with resume hints on stderr, plain-text config and session files, composition via subprocesses instead of plugins.

Target audience

Developers who live in the terminal, run local models, audit what their tools do, package software for distros, or run agents where resources are scarce. If you want MCP marketplaces, a plugin runtime, IDE panels, or per-command permission prompts, other agents build exactly that — hax deliberately doesn't, and docs/philosophy.md explains each omission and the pattern that covers the need.

If "fancy new AI tech in an old-school minimalist package" sounds like your vibe, you might like this.

Install

hax runs on Linux and macOS; on Windows, use it under WSL.

With Homebrew (macOS or Linux):

brew install oleksandrchekhovskyi/hax/hax

On Linux, download the prebuilt static binary for your architecture (x86_64 or aarch64) from the latest release, then unpack the hax binary into any directory on your PATH.

From source

Building from source gives a binary linked against your system's shared libraries instead of a static one:

git clone https://github.com/OleksandrChekhovskyi/hax.git
cd hax
scripts/install_deps.sh   # Debian/Ubuntu, Fedora, Arch, openSUSE, Alpine, macOS
make                      # the binary is now at ./build/hax
make install              # optional; may prompt for sudo

scripts/install_deps.sh installs the build dependencies — a C compiler, libcurl, jansson, meson, ninja, and pkg-config — plus fzf, which hax uses for @file completion when available. On other platforms, install those packages by hand and run make.

For hacking on hax, make symlink links the freshly built binary into ~/.local/bin so it stays on PATH across rebuilds. make lint additionally needs clang-format and clang-tidy (scripts/install_deps.sh lint installs them).

The examples below use hax as if it is on PATH; after a plain build, use ./build/hax.

Connect a provider

The easiest first run is interactive: start hax, then use /provider to see available providers and choose a model. hax remembers interactive provider, model, and effort selections.

Quick start

Run hax from the project directory you want it to work in:

hax                         # interactive REPL
hax -p "list TODOs"         # run one prompt and print the final answer
printf "explain x" | hax -p # read the prompt from stdin
hax -c                      # continue the latest session for this directory
hax --resume                # pick a past session for this directory
hax --resume=ID -p "next"   # resume a specific session in one-shot mode

Run hax --help for CLI usage. In the REPL, type /help for slash commands and shortcuts. See docs/usage.md for more detailed usage documentation.

Configuration

Every registered setting has a canonical config key and, when applicable, an HAX_* environment variable. Runtime selections made with /provider, /model, and /effort are stored separately from your config file. The more explicit the input, the higher it wins: a CLI flag beats an environment variable, which beats anything saved.

See docs/configuration.md for the file format, the full resolution order, and the setting reference.

More docs

• docs/debugging.md — trace/transcript logs, mock provider, and demo scripts.

License

MIT.