diff --git a/codegen/codegen_regex_fixes.py b/codegen/codegen_regex_fixes.py
index 5a78cb4..0c44e2b 100644
--- a/codegen/codegen_regex_fixes.py
+++ b/codegen/codegen_regex_fixes.py
@@ -4,7 +4,7 @@
 import sys
 
 
-def main(path):
+def main(path: str) -> None:
     print(f"Processing {path}")
     with open(path) as f:
         contents = f.read()
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..82aa7eb
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,2 @@
+[mypy]
+disallow_untyped_defs = True
diff --git a/src/horde_sdk/ai_horde_api/apimodels/_base.py b/src/horde_sdk/ai_horde_api/apimodels/_base.py
index 61027dc..8a0c8ef 100644
--- a/src/horde_sdk/ai_horde_api/apimodels/_base.py
+++ b/src/horde_sdk/ai_horde_api/apimodels/_base.py
@@ -76,14 +76,14 @@ class BaseImageGenerateParam(BaseModel):
     use_nsfw_censor: bool = False
 
     @field_validator("sampler_name")
-    def sampler_name_must_be_known(cls, v):
+    def sampler_name_must_be_known(cls, v: str | KNOWN_SAMPLERS) -> str | KNOWN_SAMPLERS:
         """Ensure that the sampler name is in this list of supported samplers."""
         if v not in KNOWN_SAMPLERS.__members__:
             raise ValueError(f"Unknown sampler name {v}")
         return v
 
     @field_validator("seed")
-    def seed_to_int_if_str(cls, v):
+    def seed_to_int_if_str(cls, v: str | int) -> str | int:
         """Ensure that the seed is an integer. If it is a string, convert it to an integer."""
         return str(seed_to_int(v))
 
diff --git a/src/horde_sdk/ai_horde_api/apimodels/generate/_async.py b/src/horde_sdk/ai_horde_api/apimodels/generate/_async.py
index bc73a2a..e79541a 100644
--- a/src/horde_sdk/ai_horde_api/apimodels/generate/_async.py
+++ b/src/horde_sdk/ai_horde_api/apimodels/generate/_async.py
@@ -57,7 +57,7 @@ class ImageGenerateAsyncRequest(
     replacement_filter: bool = True
 
     @model_validator(mode="before")
-    def validate_censor_nsfw(cls, values):
+    def validate_censor_nsfw(cls, values: dict) -> dict:
         if values.get("censor_nsfw", None) and values.get("nsfw", None):
             raise ValueError("censor_nsfw is only valid when nsfw is False")
         return values
diff --git a/src/horde_sdk/ai_horde_api/apimodels/generate/_pop.py b/src/horde_sdk/ai_horde_api/apimodels/generate/_pop.py
index a3ff4a5..5bbbe9c 100644
--- a/src/horde_sdk/ai_horde_api/apimodels/generate/_pop.py
+++ b/src/horde_sdk/ai_horde_api/apimodels/generate/_pop.py
@@ -79,7 +79,7 @@ class ImageGenerateJobResponse(BaseResponse):
     """The r2 upload link to use to upload this image."""
 
     @field_validator("source_processing")
-    def source_processing_must_be_known(cls, v):
+    def source_processing_must_be_known(cls, v: str | KNOWN_SOURCE_PROCESSING) -> str | KNOWN_SOURCE_PROCESSING:
         """Ensure that the source processing is in this list of supported source processing."""
         if v not in KNOWN_SOURCE_PROCESSING.__members__:
             raise ValueError(f"Unknown source processing {v}")
diff --git a/src/horde_sdk/ai_horde_api/fields.py b/src/horde_sdk/ai_horde_api/fields.py
index 40324b8..105c159 100644
--- a/src/horde_sdk/ai_horde_api/fields.py
+++ b/src/horde_sdk/ai_horde_api/fields.py
@@ -17,8 +17,11 @@ def id_as_uuid(self) -> uuid.UUID:
         return uuid.UUID(str(self.id), version=4)
 
     @field_validator("id")
-    def id_must_be_uuid(cls, v):
+    def id_must_be_uuid(cls, v: str | uuid.UUID) -> str | uuid.UUID:
         """Ensure that the ID is a valid UUID."""
+        if isinstance(v, uuid.UUID):
+            return v
+
         try:
             uuid.UUID(v, version=4)
         except ValueError as e:
diff --git a/src/horde_sdk/generic_api/apimodels.py b/src/horde_sdk/generic_api/apimodels.py
index c67e20e..834df93 100644
--- a/src/horde_sdk/generic_api/apimodels.py
+++ b/src/horde_sdk/generic_api/apimodels.py
@@ -21,7 +21,7 @@ def get_api_model_name(cls) -> str | None:
         such as for a GET request.
         """
 
-    def to_json_horde_sdk_safe(self):
+    def to_json_horde_sdk_safe(self) -> str:
         """Return the model as a JSON string, taking into account the paradigms of the horde_sdk.
 
         If you use the default json dumping behavior, you will find some rough edges, such as alias
@@ -85,7 +85,7 @@ def from_dict_or_array(cls, dict_or_array: dict | list) -> Self:
         return cls(**dict_or_array)
 
     @override
-    def to_json_horde_sdk_safe(self):
+    def to_json_horde_sdk_safe(self) -> str:
         # TODO: Is there a more pydantic way to do this?
         if self.is_array_response():
             self_array = self.get_array()
diff --git a/src/horde_sdk/generic_api/utils/swagger.py b/src/horde_sdk/generic_api/utils/swagger.py
index 289ed92..28ec44d 100644
--- a/src/horde_sdk/generic_api/utils/swagger.py
+++ b/src/horde_sdk/generic_api/utils/swagger.py
@@ -99,7 +99,7 @@ class SwaggerModelDefinitionSchemaValidation(SwaggerModelEntry):
     """The model must match at least one of the schemas in this list."""
 
     @model_validator(mode="before")
-    def one_method_specified(cls, v):
+    def one_method_specified(cls, v: dict) -> dict:
         """Ensure at least one of the validation methods is specified."""
         if not any([v.get("allOf"), v.get("oneOf"), v.get("anyOf")]):
             raise ValueError("At least one of allOf, oneOf, or anyOf must be specified.")
@@ -257,7 +257,7 @@ def get_defined_endpoints(self) -> dict[str, SwaggerEndpointMethod]:
         return return_dict
 
     @model_validator(mode="before")
-    def at_least_one_method_specified(cls, v):
+    def at_least_one_method_specified(cls, v: dict) -> dict:
         """Ensure at least one method is specified."""
         if not any(
             [
diff --git a/src/horde_sdk/scripts/write_all_payload_examples.py b/src/horde_sdk/scripts/write_all_payload_examples.py
index ac5777a..9586002 100644
--- a/src/horde_sdk/scripts/write_all_payload_examples.py
+++ b/src/horde_sdk/scripts/write_all_payload_examples.py
@@ -4,7 +4,7 @@
 from horde_sdk.generic_api.utils.swagger import SwaggerParser
 
 
-def main(*, test_data_path: Path | None = None):
+def main(*, test_data_path: Path | None = None) -> None:
     ai_horde_swagger_doc = SwaggerParser(
         swagger_doc_url=get_ai_horde_swagger_url(),
     ).get_swagger_doc()
diff --git a/src/horde_sdk/scripts/write_all_response_examples.py b/src/horde_sdk/scripts/write_all_response_examples.py
index 9c3c970..1728b2f 100644
--- a/src/horde_sdk/scripts/write_all_response_examples.py
+++ b/src/horde_sdk/scripts/write_all_response_examples.py
@@ -4,7 +4,7 @@
 from horde_sdk.generic_api.utils.swagger import SwaggerParser
 
 
-def main(*, test_data_path: Path | None = None):
+def main(*, test_data_path: Path | None = None) -> None:
     ai_horde_swagger_doc = SwaggerParser(
         swagger_doc_url=get_ai_horde_swagger_url(),
     ).get_swagger_doc()
diff --git a/src/horde_sdk/utils.py b/src/horde_sdk/utils.py
index fb83c2c..0d06ffd 100644
--- a/src/horde_sdk/utils.py
+++ b/src/horde_sdk/utils.py
@@ -1,8 +1,8 @@
 import random
 
 
-def seed_to_int(self, s=None):
-    if type(s) is int:
+def seed_to_int(s: int | str | None = None) -> int:
+    if isinstance(s, int):
         return s
     if s is None or s == "":
         # return a random int
diff --git a/tests/ai_horde_api/test_ai_horde_api_models.py b/tests/ai_horde_api/test_ai_horde_api_models.py
index cca9008..8cdb020 100644
--- a/tests/ai_horde_api/test_ai_horde_api_models.py
+++ b/tests/ai_horde_api/test_ai_horde_api_models.py
@@ -6,13 +6,13 @@
 from horde_sdk.ai_horde_api.consts import KNOWN_SAMPLERS, KNOWN_SOURCE_PROCESSING
 
 
-def test_api_endpoint():
+def test_api_endpoint() -> None:
     ImageGenerateAsyncRequest.get_api_url()
     ImageGenerateAsyncRequest.get_endpoint_subpath()
     ImageGenerateAsyncRequest.get_endpoint_url()
 
 
-def test_ImageGenerateAsyncRequest():
+def test_ImageGenerateAsyncRequest() -> None:
     test_async_request = ImageGenerateAsyncRequest(
         apikey="000000000",
         models=["Deliberate"],
diff --git a/tests/ai_horde_api/test_api_calls.py b/tests/ai_horde_api/test_api_calls.py
index 664c4c6..efc5054 100644
--- a/tests/ai_horde_api/test_api_calls.py
+++ b/tests/ai_horde_api/test_api_calls.py
@@ -26,10 +26,10 @@ def default_image_gen_request(self) -> ImageGenerateAsyncRequest:
             models=["Deliberate"],
         )
 
-    def test_AIHordeAPIClient_init(self):
+    def test_AIHordeAPIClient_init(self) -> None:
         AIHordeAPIClient()
 
-    def test_generate_async(self, default_image_gen_request: ImageGenerateAsyncRequest):
+    def test_generate_async(self, default_image_gen_request: ImageGenerateAsyncRequest) -> None:
         client = AIHordeAPIClient()
 
         image_async_response: ImageGenerateAsyncResponse | RequestErrorResponse = client.generate_image_async(
@@ -54,7 +54,7 @@ def test_generate_async(self, default_image_gen_request: ImageGenerateAsyncReque
 
         assert isinstance(cancel_response, CancelImageGenerateRequest.get_success_response_type())
 
-    def test_workers_all(self):
+    def test_workers_all(self) -> None:
         client = AIHordeAPIClient()
 
         api_request = AllWorkersDetailsRequest(type=WORKER_TYPE.image)
diff --git a/tests/ai_horde_api/test_swagger.py b/tests/ai_horde_api/test_swagger.py
index d5a8ee3..93e8548 100644
--- a/tests/ai_horde_api/test_swagger.py
+++ b/tests/ai_horde_api/test_swagger.py
@@ -2,11 +2,11 @@
 from horde_sdk.generic_api.utils.swagger import SwaggerDoc, SwaggerParser
 
 
-def test_swagger_parser_init():
+def test_swagger_parser_init() -> None:
     SwaggerParser(swagger_doc_url=get_ai_horde_swagger_url())
 
 
-def test_get_swagger_doc():
+def test_get_swagger_doc() -> None:
     parser = SwaggerParser(swagger_doc_url=get_ai_horde_swagger_url())
     doc = parser.get_swagger_doc()
     assert isinstance(doc, SwaggerDoc)
diff --git a/tests/conftest.py b/tests/conftest.py
index 82d1b29..65d3c84 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,4 +1,4 @@
-def pytest_collection_modifyitems(items):
+def pytest_collection_modifyitems(items: list) -> None:
     """Modifies test items in place to ensure test modules run in a given order."""
     MODULE_ORDER = ["tests_generic", "test_utils", "test_dynamically_check_apimodels"]
     # `test.scripts` must run first because it downloads the legacy database
diff --git a/tests/test_generic.py b/tests/test_generic.py
index 85586ee..27743ac 100644
--- a/tests/test_generic.py
+++ b/tests/test_generic.py
@@ -3,7 +3,7 @@
 from horde_sdk.generic_api import RequestErrorResponse
 
 
-def test_error_response():
+def test_error_response() -> None:
     with open("tests/test_data/RequestErrorResponse.json") as error_response_file:
         json_error_response = json.load(error_response_file)
         RequestErrorResponse(**json_error_response)
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 4cc4ee7..0c55162 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,7 +1,7 @@
 from horde_sdk.generic_api.endpoints import url_with_path
 
 
-def test_url_with_path():
+def test_url_with_path() -> None:
     example_url = "https://example.com/api/"
     example_path = "/example/path"
     example_path_no_leading_slash = "example/path"