gbax 0.12.3

Hacker-first, scriptable GBA emulator with HTTP API

gbax — Game Boy Advance you can drive.

Bring a keyboard, bring an LLM, bring both.

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gbax is an emulator you can talk to. It plays Game Boy Advance games in a window with sound and a keyboard — and in the same session, it exposes the framebuffer, memory bus, and input as an HTTP API any coding agent can reach. Use it to speedrun Pokémon Emerald with Claude Code looking over your shoulder, or to test a neurosymbolic policy against 3,500+ hand-crafted GBA environments where the level designers were genre masters. Same emulator, same session, same API. Whether you're the player or the algorithm, you're in the loop together.

Three commands

$ pip install gbax
$ gbax download "pokemon emerald"
$ gbax play emerald

Pokémon Emerald, in a window, with sound. The wheel ships a prebuilt mgba_libretro.so; no cmake, no apt-get, no $GBAX_CORE_PATH.

The cooperative loop

Launch gbax with both the keyboard surface and the HTTP API:

$ gbax play emerald --listen --plugin gbax.plugins.emerald_party
gbax HTTP API listening on http://127.0.0.1:8420
  plugin route: GET /plugins/emerald_party/party
  plugin route: GET /plugins/emerald_party/slot/{idx}

Open another terminal — yours, or your coding agent's:

$ curl -s localhost:8420/plugins/emerald_party/party | jq '.slots[0]'
{ "species": 280, "level": 11, "hp": 33, "max_hp": 33,
  "exp": 853, "friendship": 113 }

The plugin decoded Torchic's encrypted party slot for you. Want to know which menu the player is in right now? Take a screenshot in one atomic round trip:

$ curl -s -X POST localhost:8420/action \
    -H 'content-type: application/json' \
    -d '{"steps":[{"screenshot": true}]}' \
  | jq -r '.screenshots[0]' | base64 -d > /tmp/now.png

Now you, or the agent, can look at /tmp/now.png and decide what to do. The agent presses a button by sending the next action. The human can keep playing — both inputs combine via set-union, neither blocks the other.

That's the loop. The agent watches, thinks, sometimes nudges. You keep your hand on the keyboard. Together you write the next plugin, discover the next memory address, build the next algorithm.

What you get

• 3,555 ROMs in a fuzzy-searchable bundled No-Intro index. gbax download pulls from the public archive.org mirror.
• One HTTP API exposing the framebuffer, full memory bus, input, cheat codes, save states, and an atomic /action for multi-step agent plans.
• Plugins that publish their own endpoints under /plugins/<name>/.... The agent can write plugins for itself.
• State tracker — supervised memory inference. Learn game memory by labeling, not by reading per-game wikis.
• Macros, save states, cheat codes for the player who just wants to play. ~6,700 cheat codes vendored from libretro-database; no network at runtime.
• GPU shaders (crt-lottes, custom WGSL) when you want pretty.
• One pip install, one MPL-2.0 license, Linux x86_64 today.

Discovery toolkit

The AI-research / collaboration surface. Each entry links to its own docs/ page.

• HTTP API — /frame, /buttons, /memory, /step, /action (atomic multi-step), /capture_state (record labeled snapshots), /plugins/<name>/... (per-plugin namespaces), /plugins (active plugin listing).
• Plugins — Python files that hook the play loop AND publish HTTP routes. The bundled gbax.plugins.emerald_party is the canonical example: a cookbook page walks through how it was built.
• State tracker — capture / compile / refine flow. Label what's true (hp=22, scene=overworld); gbax intersects labels across captures and infers where each value lives.
• In-process Controller (automation.md) — the headless-script counterpart to plugins. Same scripting power without an HTTP round-trip.

The play surface

For the human-first reader. Each entry links to its details.

• Play window — SDL with sound, keyboard, save states. Hotkeys are documented in docs/cli.md. Headlines: Ctrl+1..9 saves a slot, Shift+1..9 loads, Left-Shift is 8× fast-forward, F12 screenshots.
• Cheats — gbax cheats <rom> lists; gbax pin <rom> F1 max-money binds; F1-F9 toggle in-game. Pins persist per ROM.
• Macros — record a button sequence with Ctrl+R, bind to any letter / digit / F-key, replay anywhere in-game.
• Shaders — gbax play <rom> --renderer=wgpu --shader=crt-lottes via the optional [gpu] extra. Full guide in docs/shaders.md.
• Save state slots survive restarts. Per-ROM, in ~/.gbax/saves/<rom-sha1>/.

Architecture

flowchart TB
    subgraph clients[" "]
        direction LR
        kbd([Keyboard])
        http([HTTP client<br/>script · LLM · shell])
    end

    subgraph cli["gbax CLI (Typer)"]
        play["gbax play"]
        serve["gbax serve"]
        other["search · download · state · macro · pin · …"]
    end

    sdl["SDL renderer<br/>window + audio + input"]
    api["FastAPI server<br/>/frame /buttons /memory /step<br/>/action /capture_state /plugins/…"]
    rt["EmulatorRuntime<br/>step · framebuffer · memory · save slots<br/>thread-safe via RLock"]
    plugins["Plugins<br/>Python @on_* handlers + @p.route()"]
    lr["LibretroCore<br/>~300 LOC cffi shim"]
    so["mgba_libretro.so"]

    kbd --> sdl
    http --> api
    play --> sdl
    play -.--> api
    serve --> api
    sdl --> rt
    api --> rt
    plugins --> rt
    plugins --> api
    rt --> lr
    lr --> so

    classDef ext fill:#eef,stroke:#33a,stroke-width:1px;
    classDef core fill:#fef9c3,stroke:#a16207,stroke-width:1px;
    class kbd,http ext;
    class so core;

• EmulatorRuntime is thread-safe via an RLock. /action and /capture_state hold the lock for their full duration; the SDL play loop blocks for the few ms each action takes, then resumes.
• The SDL window, the FastAPI server, and plugin HTTP routes are independent clients of the runtime. They don't know about each other beyond the lock.
• LibretroCore is a ~300-line cffi wrapper around the libretro ABI. Swapping in another libretro core (vba-next, gpsp) is mostly a one-line config change.

Install

pip install gbax                # default install
pip install gbax[gpu]           # adds wgpu renderer + CRT-Lottes

One command on Linux x86_64. Other platforms fall back to the sdist and need $GBAX_CORE_PATH set. Full coverage in docs/installing.md.

Status

• Alpha. v0.10.0. Works on Linux x86_64. macOS / Windows / ARM are PR-welcome.
• MPL-2.0. Same license as the underlying mGBA core.
• No ROMs bundled. gbax download pulls from the public No-Intro mirror at archive.org. Use it for games you own; respect your local laws.

Roadmap

Status	Slice
⏳	Predicate filters (@on_state_change("hp", below=20)) + ctx.wait sync API
⏳	HTTP /state — computed read of every tag in the compiled state map
⏳	GET/POST /savestate/<slot> over HTTP
⏳	xBRZ + multi-pass CRT shaders, shader hot-reload, parameter UI
⏳	macOS / Windows / aarch64 wheels
⏳	YAML user scripts — Ctrl+H runs a sequence

Past releases: see GitHub Releases.

Credits

• mGBA by endrift — the emulator core doing the actual heavy lifting. MPL-2.0.
• No-Intro — the canonical ROM-naming and SHA-1 reference.
• archive.org — hosts the No-Intro snapshot we point at by default.
• libretro-database — the cheat-code corpus we vendor.