A maximum-performance Attorney Online 2 client written in Go. Zero-fallback asset streaming, learned formats, three-tier caching, lock-free hot paths, a zero-allocation render loop and full AO2 ≥ 2.6/2.8 pairing.
Made by SyntaxNyah, because people shouldn't have to download 20 gigabytes of files to play, client lookups shouldn't take ages, and the stock AO2 client is, let's be honest, a bit slow. AsyncAO streams exactly the assets it needs, learns what formats your server ships (one probe per asset, ever), caches everything in memory and on disk, and renders without allocating.
Mayo — the AsyncAO mascot & app icon, by hlenbchan (see Credits)
- Built for speed — zero-fallback asset streaming (exactly one network probe per asset; the first probe learns what formats your server ships, so later loads resolve in <100 ns without touching the network), a three-tier cache (64 MiB GPU textures / 128 MiB raw bytes / on-disk by full URL), and a zero-allocation render loop under a 256 MiB budget. Cold-loading a 200-character server costs ~285 probes, not thousands.
- Two servers at once — every connection is a tab, and any background tab can be popped out into a floating, movable, resizable second client you watch or play alongside the main one (click it to take control; full-theme view with zoom + pan). Drag a tab downward to tear it off, Chrome-style.
- Live layout editor — drag and resize every box — viewport, log, music, IC bar, even torn-off panels — on both the default and Legacy layouts, with undo/redo and Tab-cycle. Your layout persists across sessions.
- In-app self-update — AsyncAO checks GitHub Releases on launch and updates itself in place, with a "What's new" panel. Install once; no more hand-shipped builds.
- Talks to every modern AO server — KFO-Server, tsuserver3 / tsuserverCC, Athena / Nyathena, Akashi, witches and Ferris-AO, including a dedicated KFO compatibility mode. WebSocket-only (AO2 2.11-compatible); legacy raw-TCP servers are intentionally unsupported (the lobby pins them to the bottom in black with a note to upgrade).
- Full pairing — two characters with offsets, flip and z-order, fetched in parallel so a paired message costs the same wall-clock as a solo one.
- Looks the way you want — AO2 theme support (point it at your
themes/folder andcourtroom_design.inikeeps working), chrome colour presets including eye-friendly Soft Dark and Warm, plus optional visual FX: shout punch, chatbox tint, outlines & shadows, vignette / scanlines / grain, animated chat text, reactions and inline emoji. - Accessible by default — colour emoji, broad Unicode + CJK font fallback, an OpenDyslexic font option, adjustable UI scale, and desktop toasts.
- Audio that obeys you — master + per-channel volume with per-server and
per-character mixing, per-SFX mute, an SFX picker on the IC bar, callword
alerts on a dedicated channel, and a cross-server jukebox (with history)
for the
/playlinks DJs share. - Plays well with others — cross-client character profiles, reactions and inline emoji ride a side-channel that degrades gracefully on stock AO2/webAO clients. Export a scene to MP4/WebM, or a replay to a comic strip.
- Mod & CM tools — a standalone Mod/CM dashboard (UID roster, ban/kick with a live command preview, area controls) that speaks each server family's syntax.
- Phone book & local mode — favourite and pin any server (master-list or
private), direct-connect by
ip:port/url:port/ws(s)://, or turn streaming off entirely and read from local AO2 asset folders. - Discord Rich Presence (optional, no DLL) — show server, character,
showname and area on your profile, with per-field privacy toggles. Off by
default and pure-Go IPC — no DLL, no Discord dependency, and a closed
Discord never blocks launch. A Discord-free
-tags nodiscordbuild (all Discord code stripped, settings UI included) ships alongside every release. See docs/DISCORD.md. - Quality-of-life everything — a non-blocking floating Extras box, a live
player list that groups a
/gasby area and jumps you there on a click, friend highlights and name colours, instant replay, a scene timeline, sprite preview on hover, custom window size + borderless fullscreen (F11), and much more. See docs/FEATURES.md for the full inventory.
Download the latest release —
on Windows grab asyncao-windows-x86_64-bundle.zip (unzip, run asyncao.exe),
on Linux the .AppImage (chmod +x, run). After the first install AsyncAO keeps
itself up to date in place. Prefer to build from source? See
BUILDING.md for the detailed per-OS guide.
asyncao # open the lobby
asyncao -server ws://my.private.server:50001
asyncao -debug # pprof on localhost:6060
| Doc | What's in it |
|---|---|
| BUILDING.md | Step-by-step build guide (Windows/Linux/macOS) |
| docs/ARCHITECTURE.md | Thread model, cache tiers, pipelines |
| docs/PERFORMANCE.md | Tuning, PGO capture, profiling |
| docs/BENCHMARKS.md | Recorded numbers for every gate |
| docs/adr/0001-zero-fallback-by-default.md | Why zero fallbacks |
| docs/PROTOCOL.md | The AO2 wire protocol as implemented |
| docs/DISCORD.md | Discord Rich Presence: setup, privacy, building without it |
| docs/user/lobby.md | Lobby, phone book, direct connect |
| docs/user/asset-preferences.md | Format settings guide |
| docs/user/pairing.md | Pairing guide |
| docs/user/themes.md | Migrating AO2 themes |
| docs/user/local-assets.md | No-streaming legacy mode |
Planned, not yet built:
- Eventual mobile support — native Android / iOS binaries.
- Eventual Legacy AO2 demo file converter to MP4/Video, for Archival.
- Dedicated built in theme builder so people can easily make AsyncAO themes by importing images, fonts, colours and exporting them for later. Encourages people to stop relying on QT based themes, while making the proccess streamlined and easy for anyone.
All credit to the original Attorney Online developers — AsyncAO exists because of their work and follows their protocol and conventions:
- FanatSors — creator of the original Attorney Online.
- OmniTroid — creator of the Attorney Online 2 client.
- The AttorneyOnline organization and every AO2-Client contributor — the canonical client whose protocol semantics AsyncAO mirrors
- webAO — the asset-URL conventions over HTTP come from their work
- AO-SDL — the SDL2 rendering model reference
- The whole AO community at aceattorneyonline.com
Thank you to everyone who tested AsyncAO while it was closed source — finding bugs, requesting features, and giving the feedback that shaped it: Cocoa Bean, Lala, Nightingale, Peen, Emerald, Extra7, Poki, Xocfti, Dag, CherriPop.
A special thank-you to Northgate — who backed the project, including financially, and gave the inspiration to keep going. Without that support AsyncAO wouldn't have come this far this fast.
Meet Mayo (shown at the top), AsyncAO's mascot and app icon. The client was almost called "MayAO" (Maya + AO), but became AsyncAO — we wanted more Maya representation, since the AO2 client only ever showed Phoenix and Edgeworth. So the mascot is Mayo: inspired by Maya Fey from Ace Attorney, with the Go gopher's blue palette (AsyncAO is written in Go).
Art commissioned by Nyah and illustrated by hlenbchan (Instagram @hlenbchan2) — all credit for the icon goes to them, please go support their work!
Thank you everyone for spending the time to read this.
Pull requests, bug fixes and feature requests are welcome! → github.com/SyntaxNyah/AsyncAO
AsyncAO is free software, licensed under the GNU AGPL v3 — and it's free all the way down. Every dependency is open-source under an AGPL-v3-compatible licence, with no proprietary or licence-incompatible pieces:
- Go libraries — ISC (coder/websocket),
MIT (xxhash), BSD-3
(go-sdl2,
kettek/apng,
klauspost/compress, and the
golang.org/x/*libraries), and MPL-2.0 (hashicorp/golang-lru). - Bundled engine — zlib (SDL2 / ttf / mixer); BSD (libwebp, libavif + dav1d/aom, Opus/Vorbis); the FreeType, HarfBuzz, libpng and zlib licences; LGPL (GLib, gettext, mpg123 — used as separate DLLs); and the GCC runtime under its Runtime Library Exception.
- Font — OpenDyslexic, SIL OFL 1.1.
MPL-2.0, LGPL and the GCC exception are all AGPL-compatible, so the whole stack is genuinely libre. The protocol comes from the GPLv3 AO2-Client, reimplemented clean-room in Go (protocols aren't copyrightable, and GPLv3 is AGPLv3-compatible regardless). Full per-dependency list with licences & links: docs/THIRD-PARTY-LICENSES.md.
Copyright © 2026 SyntaxNyah and the AsyncAO contributors. Because AsyncAO and all of its dependencies are AGPL-v3-compatible free software, it may be freely redistributed — including binary GitHub releases — in full compliance with the AGPL v3 and every dependency's licence. Binary releases should ship the third-party licence notices listed above alongside the LICENSE and a link to this source. See the NOTICE file for the short version.