diff --git a/handyrl/evaluation.py b/handyrl/evaluation.py
index 2d391bce..6ffca08e 100755
--- a/handyrl/evaluation.py
+++ b/handyrl/evaluation.py
@@ -3,9 +3,13 @@
 
 # evaluation of policies or planning algorithms
 
+import functools
+import importlib
 import random
+import re
 import time
 import multiprocessing as mp
+from pathlib import Path
 
 from .environment import prepare_env, make_env
 from .connection import send_recv, accept_socket_connections, connect_socket_connection
@@ -14,6 +18,11 @@
 
 network_match_port = 9876
 
+_agent_aliases = {
+    'random': RandomAgent,
+    'rulebase': RuleBasedAgent,
+}
+
 
 def view(env, player=None):
     if hasattr(env, 'view'):
@@ -141,13 +150,103 @@ def exec_network_match(env, network_agents, critic=None, show=False, game_args={
     return outcome
 
 
+def split_except_quoted_field(string, delimiter=','):
+    """Split a string ignoring quoted fields.
+
+    Example:
+        >>> agent_config = 'transformer, temperature=1.0, hoge="hoge, fuga"'
+        >>> split_except_quoted_field(agent_config, ',')
+        ['transformer',
+         'temperature=1.0',
+         'hoge="hoge, fuga"']
+
+    .. python - Split by comma and how to exclude comma from quotes in split
+        https://stackoverflow.com/a/64333329
+    """
+    delimiter_matcher = re.compile(fr"\s*{delimiter}(?=(?:[^\"']*[\"'][^\"']*[\"'])*[^\"']*$)\s*")
+    return delimiter_matcher.split(string)
+
+
+def parse_args(arg_list):
+    def _convert_dtype(value):
+        try:
+            value = eval(value)
+        except:
+            pass
+        return value
+
+    args = []
+    kwargs = {}
+    args_end_flag = False
+    for arg in arg_list:
+        arg_split = split_except_quoted_field(arg, '=')
+        if len(arg_split) == 1:  # args
+            if args_end_flag:
+                raise SyntaxError('positional argument follows keyword argument')
+            args.append(_convert_dtype(arg))
+        elif len(arg_split) == 2:  # kwargs
+            args_end_flag = True
+            key, value = arg_split
+            kwargs[key] = _convert_dtype(value)
+        else:
+            raise SyntaxError('invalid syntax')
+
+    return args, kwargs
+
+
+def register_agent(alias=None):
+    """Register a custom agent alias.
+
+    Example:
+        >>> @register_agent(alias="transformer")
+        ... class TransformerAgent:
+        ...     pass
+        >>> env = Environment({})
+        >>> agent = build_agent("transformer", env)
+
+    Note:
+        The agent class must be defined in the current context.
+        For example, if you define a class in `src/agent.py`, you need to add the following line to `main.py`.
+
+        ```python
+        import src.agent
+        ```
+    """
+
+    def _registered_class(cls, alias=None):
+        if alias is None:
+            alias = cls.__name__
+
+        # Register agent class
+        _agent_aliases[str(alias).lower()] = cls
+
+        return cls
+
+    registered_class = functools.partial(_registered_class, alias=alias)
+    return registered_class
+
+
 def build_agent(raw, env=None):
-    if raw == 'random':
-        return RandomAgent()
-    elif raw.startswith('rulebase'):
-        key = raw.split('-')[1] if '-' in raw else None
-        return RuleBasedAgent(key)
-    return None
+    agent_name, *arg_list = split_except_quoted_field(raw, ',')
+    args, kwargs = parse_args(arg_list)
+
+    if agent_name.lower() in _agent_aliases:
+        AgentClass = _agent_aliases[agent_name.lower()]
+        agent = AgentClass(*args, **kwargs)
+    elif Path(agent_name).exists():
+        # model path e.g. models/latst.pth, models/latest.pth.onnx
+        model = load_model(agent_name, env.net())
+        agent = Agent(model, *args, **kwargs)
+    elif "." not in agent_name:
+        raise ValueError(f"Unknown agent: {agent_name}")
+    else:
+        # custom agnet e.g. agents.custom_agent.CustomAgent
+        module_path, model_name = agent_name.rsplit('.', maxsplit=1)
+        module = importlib.import_module(module_path)
+        CustomAgent = getattr(module, model_name)
+        agent = CustomAgent(*args, **kwargs)
+
+    return agent
 
 
 class Evaluator:
@@ -368,9 +467,6 @@ def load_model(model_path, model=None):
 def client_mp_child(env_args, model_path, conn):
     env = make_env(env_args)
     agent = build_agent(model_path, env)
-    if agent is None:
-        model = load_model(model_path, env.net())
-        agent = Agent(model)
     NetworkAgentClient(agent, env, conn).run()
 
 
@@ -379,18 +475,11 @@ def eval_main(args, argv):
     prepare_env(env_args)
     env = make_env(env_args)
 
-    model_paths = argv[0].split(':') if len(argv) >= 1 else ['models/latest.pth']
+    model_paths = split_except_quoted_field(argv[0], ':') if len(argv) >= 1 else ['models/latest.pth']
     num_games = int(argv[1]) if len(argv) >= 2 else 100
     num_process = int(argv[2]) if len(argv) >= 3 else 1
 
-    def resolve_agent(model_path):
-        agent = build_agent(model_path, env)
-        if agent is None:
-            model = load_model(model_path, env.net())
-            agent = Agent(model)
-        return agent
-
-    main_agent = resolve_agent(model_paths[0])
+    main_agent = build_agent(model_paths[0])
     critic = None
 
     print('%d process, %d games' % (num_process, num_games))
@@ -399,7 +488,7 @@ def resolve_agent(model_path):
     print('seed = %d' % seed)
 
     opponent = model_paths[1] if len(model_paths) > 1 else 'random'
-    agents = [main_agent] + [resolve_agent(opponent) for _ in range(len(env.players()) - 1)]
+    agents = [main_agent] + [build_agent(opponent) for _ in range(len(env.players()) - 1)]
 
     evaluate_mp(env, agents, critic, env_args, {'default': {}}, num_process, num_games, seed)