a2kit

A passive AION 2 protocol toolkit, library and CLI (capture, decode, telemetry, analysis) with a structured a2log session format. No injection. No Npcap/WinPcap required.

CLI

Download a2k for your system from the releases, or install it as a CLI tool:

go install github.com/nuriland/a2kit/cmd/a2k@latest

On Linux, a2k needs libpcap to capture live, and libpcap-dev to build. A build without cgo reads recordings, but cannot capture.

Use

a2k help                                      # list all available commands
a2k watch                                     # what happens in the game, live
a2k record -log fight.jsonl                   # save the game's session
a2k show fight.pcap                           # read the saved game session
a2k export fight.pcap -o fight.jsonl          # a log to share
a2k timeline fight.pcap -o fight.trace.json   # a timeline reconstruction via ui.perfetto.dev
a2k stats fight.pcap                          # which message types came, and which a2k decodes

Example usage of a2k show:

   21.050  Hit        actor=37365 target=15943 skill=11020000 damage=36 type=2 scalar=10000

From the server list on, before a world server is picked:

    1.006  Servers    list=[1301:LIVE_Light_001 3245/7500 restricted 1302:LIVE_Light_002 2374/7000 ...]
    5.015  Redirect   server=1304 host=10.0.0.2 port=13328

Live capture

watch and record find the game's connection by themselves. Needs priviledged access to run on all platforms (Win, Linux, MacOS).

Windows

• Doesn't require Npcap or WinPcap installed, it runs on native pktmon monitor.
• It captures on every adapter at once (nics), a VPN's tunnel included, by default. a2k adapters lists the adapters.

Recording and sharing

a2k record saves a session two ways, and can do both at once:

• -log fight.jsonl, a log of the game's messages only, with their raw bytes
• fight.pcap, a recording of all the adapter's TCP traffic. DO NOT SHARE THESE PUBLICLY.

The log, a2k export and a2k timeline leave out the messages that name your account (Login, Account, Characters). -account keeps them. What show and watch print still includes them.

a2log

a2k record -log and a2k export write an a2log file format.

{"schema":"a2log/v0.1","decoder":"github.com/nuriland/a2kit@v0.3.0","source":{"kind":"pcap","path":"fight.pcap"},"t0":"2026-09-23T18:00:00.123Z"}
{"t":0,"opcode":"04 38","flags":["server"],"src":"10.0.0.2:13328","dst":"10.0.0.1:10000","payload":"x3wEAPWjAuAmqAAAAkvtn0EBAAAAkE4kAQA="}
{"t":51,"opcode":"42 36","flags":["server"],"src":"10.0.0.2:13328","dst":"10.0.0.1:10000","payload":"x3wAAw=="}

The header:

key
schema	a2log/v0.1
decoder	the a2kit module and version that wrote the log
source	kind is pcap, live or feed -- path is the file, or the adapter
t0	the first message's time, UTC

Each message:

key
t	milliseconds after t0, negative for a message completed out of order
opcode	the message type, two bytes in wire order
flags	server or client, then lz4, bundled, resynced
src, dst	the endpoints
payload	the bytes after the type, base64

a2k show fight.jsonl                                                                   # what the log says
jq -r 'select(.opcode) | .opcode' fight.jsonl | sort | uniq -c | sort -rn              # messages by type
jq -c 'select(.opcode == "04 38")' fight.jsonl                                         # the hits
jq -r 'select(.opcode == "04 38") | .payload' fight.jsonl | head -1 | base64 -d | xxd  # one hit's bytes

a2k show on the three lines above:

    0.000  Hit        actor=37365 target=15943 skill=11020000 damage=36 type=2 scalar=10000
    0.051  Death      entity=15943 flag=3

a2kit.Open reads a log the same way it reads a recording. a2log.NewReader reads one on its own, and gives the frames game.Parse takes:

r, err := a2log.NewReader(file)
if err != nil {
	return err
}
for f, err := range r.Frames() {
	if err != nil {
		return err
	}
	e, _ := game.Parse(f) // nil when game does not read it
	if hit, ok := e.(game.Hit); ok {
		fmt.Println(hit.Actor, hit.Target, hit.Damage)
	}
}

Warning: A log holds what the game sent, players' names among it. Your account ID and character list are left out unless it was written with -account.

As a library

go get github.com/nuriland/a2kit

r, err := a2kit.Open("fight.pcap", a2kit.Config{})
if err != nil {
	return err
}
defer r.Close()

for m, err := range r.Messages() {
	if err != nil {
		return err
	}
	if hit, ok := m.Event.(game.Hit); ok {
		fmt.Println(hit.Actor, hit.Target, hit.Skill, hit.Damage)
	}
}
fmt.Printf("%+v\n", r.Summary()) // how many were decoded, the game's connection, what was lost

Work in progress.