diff --git a/src/nexusrpc/_service.py b/src/nexusrpc/_service.py
index f62eb67..f97ac59 100644
--- a/src/nexusrpc/_service.py
+++ b/src/nexusrpc/_service.py
@@ -8,6 +8,7 @@
 
 import dataclasses
 import typing
+import urllib.parse
 from collections.abc import Mapping
 from dataclasses import dataclass
 from typing import (
@@ -29,6 +30,24 @@
 )
 
 
+def _validate_nexus_name(name: str) -> None:
+    """Validate that a name is valid for use as a Nexus service or operation name.
+
+    Per the spec: "The service name and operation name MUST not be empty and
+    may contain any arbitrary character sequence as long as they're encoded
+    into the URL."
+
+    Raises:
+        ValueError: If the name is empty, whitespace-only, or cannot be URL-encoded.
+    """
+    if not name or not name.strip():
+        raise ValueError("must not be empty")
+    try:
+        _ = urllib.parse.quote(name, safe="")
+    except (UnicodeEncodeError, KeyError) as e:
+        raise ValueError("contains characters that cannot be URL-encoded") from e
+
+
 @dataclass
 class Operation(Generic[InputT, OutputT]):
     """Defines a Nexus operation in a Nexus service definition.
@@ -67,10 +86,12 @@ class OperationDefinition(Generic[InputT, OutputT]):
     def from_operation(
         cls, operation: Operation[InputT, OutputT]
     ) -> OperationDefinition[InputT, OutputT]:
-        if not operation.name:
+        try:
+            _validate_nexus_name(operation.name)
+        except ValueError as e:
             raise ValueError(
-                f"Operation has no name (method_name is '{operation.method_name}')"
-            )
+                f"Operation name {operation.name!r} {e} (method_name is '{operation.method_name}')"
+            ) from e
         if not operation.method_name:
             raise ValueError(f"Operation '{operation.name}' has no method name")
         if not operation.input_type:
@@ -126,9 +147,12 @@ class AnotherService:
     """
 
     def decorator(cls: type[ServiceT]) -> type[ServiceT]:
-        if name is not None and not name:
-            raise ValueError("Service name must not be empty.")
-        defn = ServiceDefinition.from_class(cls, name or cls.__name__)
+        service_name = name if name is not None else cls.__name__
+        try:
+            _validate_nexus_name(service_name)
+        except ValueError as e:
+            raise ValueError(f"Service name {service_name!r} {e}.")
+        defn = ServiceDefinition.from_class(cls, service_name)
         set_service_definition(cls, defn)
 
         # In order for callers to refer to operation definitions at run-time, a decorated user
@@ -231,10 +255,18 @@ def from_class(user_class: type[ServiceT], name: str) -> ServiceDefinition:
 
     def _validation_errors(self) -> list[str]:
         errors = []
-        if not self.name:
-            errors.append("Service has no name")
-        seen_method_names = set()
+        # Validate service name
+        try:
+            _validate_nexus_name(self.name)
+        except ValueError as e:
+            errors.append(f"Service name {self.name!r} {e}")
+        # Validate operation names and check for duplicate method names
+        seen_method_names: set[str] = set()
         for op_defn in self.operation_definitions.values():
+            try:
+                _validate_nexus_name(op_defn.name)
+            except ValueError as e:
+                errors.append(f"Operation name {op_defn.name!r} {e}")
             if op_defn.method_name in seen_method_names:
                 errors.append(
                     f"Operation method name '{op_defn.method_name}' is not unique"
diff --git a/tests/service_definition/test_service_decorator_validation.py b/tests/service_definition/test_service_decorator_validation.py
index 05f76a4..9809a37 100644
--- a/tests/service_definition/test_service_decorator_validation.py
+++ b/tests/service_definition/test_service_decorator_validation.py
@@ -42,3 +42,112 @@ def test_operation_validation(
         match=str(test_case.expected_error),
     ):
         nexusrpc.service(test_case.Contract)
+
+
+def test_empty_service_name_raises():
+    """Empty string passed to @service(name='') should raise."""
+    with pytest.raises(ValueError, match=r"Service name '' must not be empty"):
+
+        @nexusrpc.service(name="")
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str]
+
+
+def test_whitespace_only_service_name_raises():
+    """Whitespace-only service name should raise."""
+    with pytest.raises(ValueError, match=r"Service name '   ' must not be empty"):
+
+        @nexusrpc.service(name="   ")
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str]
+
+
+def test_non_url_encodable_service_name_raises():
+    """Service name with non-URL-encodable characters should raise."""
+    with pytest.raises(
+        ValueError,
+        match=r"Service name .* contains characters that cannot be URL-encoded",
+    ):
+
+        @nexusrpc.service(name="invalid\ud800surrogate")
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str]
+
+
+def test_valid_service_name_with_special_chars_succeeds():
+    """Service names with URL-encodable special characters should succeed."""
+
+    @nexusrpc.service(name="my service")
+    class ServiceWithSpace:
+        op: nexusrpc.Operation[str, str]
+
+    _ = ServiceWithSpace
+
+    @nexusrpc.service(name="service/with/slashes")
+    class ServiceWithSlashes:
+        op: nexusrpc.Operation[str, str]
+
+    _ = ServiceWithSlashes
+
+    @nexusrpc.service(name="日本語サービス")
+    class ServiceWithUnicode:
+        op: nexusrpc.Operation[str, str]
+
+    _ = ServiceWithUnicode
+
+    @nexusrpc.service(name="service?query=value")
+    class ServiceWithQueryChars:
+        op: nexusrpc.Operation[str, str]
+
+    _ = ServiceWithQueryChars
+
+
+def test_empty_operation_name_raises():
+    """Empty operation name should raise."""
+    with pytest.raises(ValueError, match=r"Operation name '' must not be empty"):
+
+        @nexusrpc.service
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str] = nexusrpc.Operation(name="")
+
+
+def test_whitespace_only_operation_name_raises():
+    """Whitespace-only operation name should raise."""
+    with pytest.raises(ValueError, match=r"Operation name '   ' must not be empty"):
+
+        @nexusrpc.service
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str] = nexusrpc.Operation(name="   ")
+
+
+def test_non_url_encodable_operation_name_raises():
+    """Operation name with non-URL-encodable characters should raise."""
+    with pytest.raises(
+        ValueError,
+        match=r"Operation name .* contains characters that cannot be URL-encoded",
+    ):
+
+        @nexusrpc.service
+        class MyService:  # pyright: ignore[reportUnusedClass]
+            op: nexusrpc.Operation[str, str] = nexusrpc.Operation(
+                name="invalid\ud800surrogate"
+            )
+
+
+def test_valid_operation_name_with_special_chars_succeeds():
+    """Operation names with URL-encodable special characters should succeed."""
+
+    @nexusrpc.service
+    class MyService:
+        op_with_space: nexusrpc.Operation[str, str] = nexusrpc.Operation(
+            name="my operation"
+        )
+        op_with_slash: nexusrpc.Operation[str, str] = nexusrpc.Operation(
+            name="op/with/slashes"
+        )
+        op_unicode: nexusrpc.Operation[str, str] = nexusrpc.Operation(name="日本語操作")
+        op_query: nexusrpc.Operation[str, str] = nexusrpc.Operation(
+            name="op?param=value"
+        )
+
+    _ = MyService
diff --git a/tests/test_type_errors.py b/tests/test_type_errors.py
index 98a09a1..76c0a0a 100644
--- a/tests/test_type_errors.py
+++ b/tests/test_type_errors.py
@@ -83,7 +83,7 @@ def _test_type_errors(
 
 def _has_type_error_assertions(test_file: Path) -> bool:
     """Check if a file contains any type error assertions."""
-    with open(test_file) as f:
+    with open(test_file, encoding="utf-8") as f:
         return any(
             re.search(r"# assert-type-error-\w+:", line) for line in f.readlines()
         )
@@ -93,7 +93,7 @@ def _get_expected_errors(test_file: Path, type_checker: str) -> dict[int, str]:
     """Parse expected type errors from comments in a file for the specified type checker."""
     expected_errors = {}
 
-    with open(test_file) as f:
+    with open(test_file, encoding="utf-8") as f:
         lines = zip(itertools.count(1), f)
         for line_num, line in lines:
             if match := re.search(