diff --git a/eppo_client/rules.py b/eppo_client/rules.py
index 7f9859c..5f706c5 100644
--- a/eppo_client/rules.py
+++ b/eppo_client/rules.py
@@ -1,11 +1,13 @@
+import json
 import numbers
 import re
-import semver
 from enum import Enum
 from typing import Any, List
 
+import semver
+
 from eppo_client.models import SdkBaseModel
-from eppo_client.types import ConditionValueType, SubjectAttributes
+from eppo_client.types import AttributeType, ConditionValueType, SubjectAttributes
 
 
 class OperatorType(Enum):
@@ -49,20 +51,20 @@ def evaluate_condition(
     if subject_value is not None:
         if condition.operator == OperatorType.MATCHES:
             return isinstance(condition.value, str) and bool(
-                re.search(condition.value, str(subject_value))
+                re.search(condition.value, to_string(subject_value))
             )
-        if condition.operator == OperatorType.NOT_MATCHES:
+        elif condition.operator == OperatorType.NOT_MATCHES:
             return isinstance(condition.value, str) and not bool(
-                re.search(condition.value, str(subject_value))
+                re.search(condition.value, to_string(subject_value))
             )
         elif condition.operator == OperatorType.ONE_OF:
-            return isinstance(condition.value, list) and str(subject_value) in [
+            return isinstance(condition.value, list) and to_string(subject_value) in [
                 str(value) for value in condition.value
             ]
         elif condition.operator == OperatorType.NOT_ONE_OF:
-            return isinstance(condition.value, list) and str(subject_value) not in [
-                str(value) for value in condition.value
-            ]
+            return isinstance(condition.value, list) and to_string(
+                subject_value
+            ) not in [str(value) for value in condition.value]
         else:
             # Numeric operator: value could be numeric or semver.
             if isinstance(subject_value, numbers.Number):
@@ -119,3 +121,13 @@ def compare_semver(
         return semver.compare(attribute_value, condition_value) <= 0
 
     return False
+
+
+def to_string(value: AttributeType) -> str:
+    if isinstance(value, str):
+        return value
+    elif isinstance(value, bool):
+        return "true" if value else "false"
+    elif isinstance(value, float):
+        return f"{value:.0f}" if value.is_integer() else str(value)
+    return json.dumps(value)
diff --git a/eppo_client/types.py b/eppo_client/types.py
index 07f126a..09d69b3 100644
--- a/eppo_client/types.py
+++ b/eppo_client/types.py
@@ -1,7 +1,7 @@
 from typing import Dict, List, Union
 
 ValueType = Union[str, int, float, bool]
-AttributeType = Union[str, int, float, bool]
+AttributeType = Union[str, int, float, bool, None]
 ConditionValueType = Union[AttributeType, List[AttributeType]]
 SubjectAttributes = Dict[str, AttributeType]
 Action = str
diff --git a/test/rules_test.py b/test/rules_test.py
index 049dbfc..679bffc 100644
--- a/test/rules_test.py
+++ b/test/rules_test.py
@@ -4,6 +4,7 @@
     Condition,
     evaluate_condition,
     matches_rule,
+    to_string,
 )
 
 greater_than_condition = Condition(operator=OperatorType.GT, value=10, attribute="age")
@@ -137,10 +138,22 @@ def test_evaluate_condition_matches():
         Condition(operator=OperatorType.MATCHES, value="^test.*", attribute="email"),
         {"email": "test@example.com"},
     )
+    assert evaluate_condition(
+        Condition(operator=OperatorType.MATCHES, value="true", attribute="flag"),
+        {"flag": True},
+    )
+    assert evaluate_condition(
+        Condition(operator=OperatorType.MATCHES, value="false", attribute="flag"),
+        {"flag": False},
+    )
     assert not evaluate_condition(
         Condition(operator=OperatorType.MATCHES, value="^test.*", attribute="email"),
         {"email": "example@test.com"},
     )
+    assert not evaluate_condition(
+        Condition(operator=OperatorType.MATCHES, value="False", attribute="flag"),
+        {"flag": False},
+    )
 
 
 def test_evaluate_condition_matches_partial():
@@ -348,10 +361,10 @@ def test_evaluate_condition_one_of_int():
 
 def test_evaluate_condition_one_of_boolean():
     one_of_condition_boolean = Condition(
-        operator=OperatorType.ONE_OF, value=[True, False], attribute="status"
+        operator=OperatorType.ONE_OF, value=["true", "false"], attribute="status"
     )
     assert evaluate_condition(one_of_condition_boolean, {"status": False})
-    assert evaluate_condition(one_of_condition_boolean, {"status": "False"})
+    assert evaluate_condition(one_of_condition_boolean, {"status": "false"})
     assert not evaluate_condition(one_of_condition_boolean, {"status": "Maybe"})
     assert not evaluate_condition(one_of_condition_boolean, {"status": 0})
     assert not evaluate_condition(one_of_condition_boolean, {"status": 1})
@@ -391,3 +404,26 @@ def test_is_not_null_operator():
     assert not evaluate_condition(is_not_null_condition, {"size": None})
     assert evaluate_condition(is_not_null_condition, {"size": 10})
     assert not evaluate_condition(is_not_null_condition, {})
+
+
+def test_to_string_string():
+    assert to_string("test") == "test"
+
+
+def test_to_string_int():
+    assert to_string(10) == "10"
+
+
+def test_to_string_float():
+    assert to_string(10.5) == "10.5"
+    assert to_string(10.0) == "10"
+    assert to_string(123456789.0) == "123456789"
+
+
+def test_to_string_bool():
+    assert to_string(True) == "true"
+    assert to_string(False) == "false"
+
+
+def test_to_string_null():
+    assert to_string(None) == "null"