diff --git a/ircrobots/interface.py b/ircrobots/interface.py
new file mode 100644
index 0000000..121f6e1
--- /dev/null
+++ b/ircrobots/interface.py
@@ -0,0 +1,52 @@
+from typing import Optional
+from enum import IntEnum
+from dataclasses import dataclass
+
+from ircstates import Server
+from irctokens import Line
+
+from .ircv3 import Capability
+
+@dataclass
+class ConnectionParams(object):
+    nickname: str
+    host:     str
+    port:     int
+    ssl:      bool
+
+    username: Optional[str] = None
+    realname: Optional[str] = None
+    bindhost: Optional[str] = None
+
+class SendPriority(IntEnum):
+    HIGH   = 0
+    MEDIUM = 10
+    LOW    = 20
+    DEFAULT = MEDIUM
+
+class PriorityLine(object):
+    def __init__(self, priority: int, line: Line):
+        self.priority = priority
+        self.line = line
+    def __lt__(self, other: "PriorityLine") -> bool:
+        return self.priority < other.priority
+
+class IServer(Server):
+    params:  ConnectionParams
+
+    async def send_raw(self, line: str, priority=SendPriority.DEFAULT):
+        pass
+    async def send(self, line: Line, priority=SendPriority.DEFAULT):
+        pass
+
+    def set_throttle(self, rate: int, time: float):
+        pass
+
+    async def connect(self, params: ConnectionParams):
+        pass
+
+    async def queue_capability(self, cap: Capability):
+        pass
+
+    async def line_written(self, line: Line):
+        pass
diff --git a/ircrobots/server.py b/ircrobots/server.py
index 0540fc0..6281c44 100644
--- a/ircrobots/server.py
+++ b/ircrobots/server.py
@@ -6,41 +6,18 @@ from enum        import IntEnum
 from dataclasses import dataclass
 
 from asyncio_throttle import Throttler
-from ircstates        import Server as BaseServer
 from ircstates        import Emit
 from irctokens        import build, Line, tokenise
 
-from .ircv3 import Capability, CAPS
+from .ircv3     import Capability, CAPS
+from .interface import ConnectionParams, IServer, PriorityLine, SendPriority
+
 sc = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)
 
 THROTTLE_RATE = 4 # lines
 THROTTLE_TIME = 2 # seconds
 
-@dataclass
-class ConnectionParams(object):
-    nickname: str
-    host:     str
-    port:     int
-    ssl:      bool
-
-    username: Optional[str] = None
-    realname: Optional[str] = None
-    bindhost: Optional[str] = None
-
-class SendPriority(IntEnum):
-    HIGH   = 0
-    MEDIUM = 10
-    LOW    = 20
-    DEFAULT = MEDIUM
-
-class PriorityLine(object):
-    def __init__(self, priority: int, line: Line):
-        self.priority = priority
-        self.line = line
-    def __lt__(self, other: "PriorityLine") -> bool:
-        return self.priority < other.priority
-
-class Server(BaseServer):
+class Server(IServer):
     _reader: asyncio.StreamReader
     _writer: asyncio.StreamWriter
     params:  ConnectionParams
@@ -93,9 +70,8 @@ class Server(BaseServer):
         if matches:
             self._requested_caps = matches
             await self.send(build("CAP", ["REQ", " ".join(matches)]))
-    async def _cap_ack(self, line: Line):
-        caps = line.params[2].split(" ")
-        for cap in caps:
+    async def _cap_ack(self, emit: Emit):
+        for cap in (emit.tokens or []):
             if cap in self._requested_caps:
                 self._requested_caps.remove(cap)
         if not self._requested_caps:
@@ -106,7 +82,7 @@ class Server(BaseServer):
             if emit.subcommand == "LS" and emit.finished:
                 await self._cap_ls_done()
             elif emit.subcommand in ["ACK", "NAK"]:
-                await self._cap_ack(line)
+                await self._cap_ack(emit)
 
     async def _on_read_line(self, line: Line):
         pass
diff --git a/requirements.txt b/requirements.txt
index 18f582f..6810584 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,3 @@
-ircstates        ==0.8.0
+ircstates        ==0.8.1
 asyncio-throttle ==1.0.1
+dataclasses      ==0.6