diff --git a/phasmplatform/common/container.py b/phasmplatform/common/container.py
new file mode 100644
index 0000000..07985dc
--- /dev/null
+++ b/phasmplatform/common/container.py
@@ -0,0 +1,15 @@
+from typing import List
+
+from .image import Image
+from .method import Method
+
+
+class Container:
+    __slots__ = ('image', 'methods', )
+
+    image: Image
+    methods: List[Method]
+
+    def __init__(self, image: Image, methods: List[Method]) -> None:
+        self.image = image
+        self.methods = methods
diff --git a/phasmplatform/common/image.py b/phasmplatform/common/image.py
new file mode 100644
index 0000000..2452d1a
--- /dev/null
+++ b/phasmplatform/common/image.py
@@ -0,0 +1,7 @@
+class Image:
+    __slots__ = ('hash', )
+
+    hash: str
+
+    def __init__(self, hash: str) -> None:
+        self.hash = hash
diff --git a/phasmplatform/common/method.py b/phasmplatform/common/method.py
new file mode 100644
index 0000000..de2d198
--- /dev/null
+++ b/phasmplatform/common/method.py
@@ -0,0 +1,28 @@
+from typing import List
+
+
+from .valuetype import ValueType
+
+
+class MethodArgument:
+    __slots__ = ('name', 'value_type', )
+
+    name: str
+    value_type: ValueType
+
+    def __init__(self, name: str, value_type: ValueType) -> None:
+        self.name = name
+        self.value_type = value_type
+
+
+class Method:
+    __slots__ = ('name', 'args', 'return_type', )
+
+    name: str
+    args: List[MethodArgument]
+    return_type: ValueType
+
+    def __init__(self, name: str, args: List[MethodArgument], return_type: ValueType) -> None:
+        self.name = name
+        self.args = args
+        self.return_type = return_type
diff --git a/phasmplatform/common/value.py b/phasmplatform/common/value.py
index 1ba44ea..61a59c9 100644
--- a/phasmplatform/common/value.py
+++ b/phasmplatform/common/value.py
@@ -1,26 +1,22 @@
-from typing import Any, Generic, TypeVar
+from typing import Any, Union
 
-T = TypeVar('T')
+from .valuetype import ValueType
+
+ValueData = Union[None, bytes]
 
 
-class BaseValue(Generic[T]):
-    __slots__ = ('data', )
+class Value:
+    __slots__ = ('value_type', 'data', )
 
-    data: T
+    value_type: ValueType
+    data: ValueData
 
-    def __init__(self, data: T) -> None:
+    def __init__(self, value_type: ValueType, data: ValueData) -> None:
+        self.value_type = value_type
         self.data = data
 
     def __eq__(self, other: Any) -> bool:
-        return self.__class__ is other.__class__ and self.data == other.data
+        return self.value_type is other.value_type and self.data == other.data
 
     def __repr__(self) -> str:
-        return f'{self.__class__.__name__}({repr(self.data)})'
-
-
-class UntypedValue(BaseValue[Any]):
-    pass
-
-
-class BytesValue(BaseValue[bytes]):
-    pass
+        return f'Value(valuetype.{self.value_type.name}, {repr(self.data)})'
diff --git a/phasmplatform/common/valuetype.py b/phasmplatform/common/valuetype.py
new file mode 100644
index 0000000..8d01684
--- /dev/null
+++ b/phasmplatform/common/valuetype.py
@@ -0,0 +1,12 @@
+class ValueType:
+    __slots__ = ('name', )
+
+    name: str
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+
+
+bytes = ValueType('bytes')
+
+none = ValueType('none')
diff --git a/phasmplatform/worker/__main__.py b/phasmplatform/worker/__main__.py
index 5d4e366..5dc30ae 100644
--- a/phasmplatform/worker/__main__.py
+++ b/phasmplatform/worker/__main__.py
@@ -1,15 +1,28 @@
-from typing import Any
-
 import sys
 
+from phasmplatform.common import valuetype
 from phasmplatform.common.config import from_toml
+from phasmplatform.common.method import Method, MethodArgument
 from phasmplatform.common.router import StdOutRouter
-from phasmplatform.common.value import BaseValue, BytesValue
+from phasmplatform.common.value import Value
 
-from .runners.base import BaseRunner
+from .runners.base import RunnerInterface
 from .runners.wasmtime import WasmTimeRunner
 
 
+def somefunc(runner: RunnerInterface) -> None:
+    inp = Value(valuetype.bytes, b'Hello, world!')
+    print('inp', inp)
+
+    def on_respond(out: Value) -> None:
+        print('out', out)
+        assert out == inp
+
+    echo = Method('echo', [MethodArgument('msg', valuetype.bytes)], valuetype.bytes)
+
+    runner.do_call(echo, [inp], on_respond)
+
+
 def main() -> int:
     with open('config.toml', 'rb') as fil:
         config = from_toml(fil)
@@ -18,26 +31,17 @@ def main() -> int:
 
     stdout_router = StdOutRouter()
 
-    foo: BaseRunner
-
     with open('/home/johan/projects/idea/phasm/examples/platform.wasm', 'rb') as fil:
         foo = WasmTimeRunner(stdout_router, fil.read())
 
-    namespace = b'test-namespace'
-    topic = b'test-topic'
-    kind = b'test-kind'
-    body = b'test-body'
+    # namespace = b'test-namespace'
+    # topic = b'test-topic'
+    # kind = b'test-kind'
+    # body = b'test-body'
 
-    foo.handle_message(namespace, topic, kind, body)
+    # foo.handle_message(namespace, topic, kind, body)
 
-    inp = BytesValue(b'Hello, world!')
-    print('inp', inp)
-
-    def on_respond(out: BaseValue[Any]) -> None:
-        print('out', out)
-        assert out == inp
-
-    foo.do_call('echo', [inp], on_respond)
+    somefunc(foo)
 
     return 0
 
diff --git a/phasmplatform/worker/runners/base.py b/phasmplatform/worker/runners/base.py
index 02199b4..dd20aa9 100644
--- a/phasmplatform/worker/runners/base.py
+++ b/phasmplatform/worker/runners/base.py
@@ -1,9 +1,18 @@
-from typing import TextIO
+from typing import Callable, List, TextIO
 
 from phasmplatform.common.router import BaseRouter
+from phasmplatform.common.method import Method
+from phasmplatform.common.value import Value
 
 
-class BaseRunner:
+class RunnerInterface:
+    __slots__ = ('router', )
+
+    def do_call(self, method: Method, args: List[Value], on_result: Callable[[Value], None]) -> None:
+        raise NotImplementedError
+
+
+class BaseRunner(RunnerInterface):
     __slots__ = ('router', )
 
     router: BaseRouter
diff --git a/phasmplatform/worker/runners/wasmtime.py b/phasmplatform/worker/runners/wasmtime.py
index 45de585..e3d1a41 100644
--- a/phasmplatform/worker/runners/wasmtime.py
+++ b/phasmplatform/worker/runners/wasmtime.py
@@ -1,12 +1,15 @@
-from typing import Any, Callable, List, Union
+from typing import Callable, List, Union
 
 import ctypes
 import struct
 
 import wasmtime
 
+from phasmplatform.common import valuetype
+from phasmplatform.common.method import Method
 from phasmplatform.common.router import BaseRouter
-from phasmplatform.common.value import BaseValue, BytesValue, UntypedValue
+from phasmplatform.common.value import Value
+from phasmplatform.common.valuetype import ValueType
 from .base import BaseRunner
 
 
@@ -66,20 +69,39 @@ class WasmTimeRunner(BaseRunner):
 
         return raw[ptr + 4:ptr + 4 + length]
 
-    def convert_value(self, val: BaseValue[Any]) -> Union[int, float]:
-        if isinstance(val, BytesValue):
+    def value_to_wasm(self, val: Value) -> Union[None, int, float]:
+        if val.value_type is valuetype.bytes:
+            assert isinstance(val.data, bytes)  # type hint
             return self.alloc_bytes(val.data)
 
         raise NotImplementedError(val)
 
-    def do_call(self, method_name: str, args: List[BaseValue[Any]], callback: Callable[[BaseValue[Any]], None]) -> None:
-        method = self.exports[method_name]
-        assert isinstance(method, wasmtime.Func)
+    def value_from_wasm(self, value_type: ValueType, val: Union[None, int, float]) -> Value:
+        if value_type is valuetype.bytes:
+            assert isinstance(val, int)   # typ hint
+            return Value(valuetype.bytes, self.read_bytes(val))
 
-        act_args = [self.convert_value(x) for x in args]
-        result = method(self.store, *act_args)
+        raise NotImplementedError(value_type, val)
 
-        callback(UntypedValue(result))  # TODO: This returns a bytes pointer, but we can't detect that in advance
+    def do_call(self, method: Method, args: List[Value], on_result: Callable[[Value], None]) -> None:
+        wasm_method = self.exports[method.name]
+        assert isinstance(wasm_method, wasmtime.Func)
+
+        act_args = [self.value_to_wasm(x) for x in args]
+        result = wasm_method(self.store, *act_args)
+        assert result is None or isinstance(result, (int, float, ))  # type hint
+        on_result(self.value_from_wasm(method.return_type, result))
+
+        # callback(UntypedValue(result))  # TODO: This returns a bytes pointer, but we can't detect that in advance
+
+    # def do_call(self, method_name: str, args: List[BaseValue[Any]], callback: Callable[[BaseValue[Any]], None]) -> None:
+    #     method = self.exports[method_name]
+    #     assert isinstance(method, wasmtime.Func)
+
+    #     act_args = [self.convert_value(x) for x in args]
+    #     result = method(self.store, *act_args)
+
+    #     callback(UntypedValue(result))  # TODO: This returns a bytes pointer, but we can't detect that in advance
 
     def handle_message(self, namespace: bytes, topic: bytes, kind: bytes, body: bytes) -> None:
         namespace_ptr = self.alloc_bytes(namespace)