diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 776536e47..9abd03d09 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -44,6 +44,18 @@ repos:
       - id: isort
         entry: bash -c "cd backend && isort ."
         types: [python]
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v1.5.1
+    hooks:
+      - id: mypy
+        types_or: [python, spec]
+        files: "^backend/capellacollab"
+        exclude: "^backend/capellacollab/alembic/"
+        args: [--config-file=./backend/pyproject.toml]
+        additional_dependencies:
+          - fastapi
+          - pydantic
+          - sqlalchemy
   - repo: local
     hooks:
       - id: pylint
diff --git a/backend/capellacollab/__main__.py b/backend/capellacollab/__main__.py
index eaab432d6..4f310aafa 100644
--- a/backend/capellacollab/__main__.py
+++ b/backend/capellacollab/__main__.py
@@ -21,6 +21,9 @@
 from capellacollab.core import logging as core_logging
 from capellacollab.core.database import engine, migration
 from capellacollab.core.logging import exceptions as logging_exceptions
+from capellacollab.projects.toolmodels import (
+    exceptions as toolmodels_exceptions,
+)
 from capellacollab.projects.toolmodels.backups import (
     exceptions as backups_exceptions,
 )
@@ -133,6 +136,7 @@ async def healthcheck():
 
 def register_exceptions():
     tools_exceptions.register_exceptions(app)
+    toolmodels_exceptions.register_exceptions(app)
     git_exceptions.register_exceptions(app)
     gitlab_exceptions.register_exceptions(app)
     git_handler_exceptions.register_exceptions(app)
diff --git a/backend/capellacollab/alembic/versions/1a4208c18909_make_tool_name_required.py b/backend/capellacollab/alembic/versions/1a4208c18909_make_tool_name_required.py
new file mode 100644
index 000000000..e76ea666e
--- /dev/null
+++ b/backend/capellacollab/alembic/versions/1a4208c18909_make_tool_name_required.py
@@ -0,0 +1,27 @@
+# SPDX-FileCopyrightText: Copyright DB Netz AG and the capella-collab-manager contributors
+# SPDX-License-Identifier: Apache-2.0
+
+"""Make tool name required
+
+Revision ID: 1a4208c18909
+Revises: d8cf851562cd
+Create Date: 2023-09-19 11:25:16.343948
+
+"""
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "1a4208c18909"
+down_revision = "d8cf851562cd"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.alter_column(
+        "tools",
+        "name",
+        existing_type=sa.String(),
+        nullable=False,
+    )
diff --git a/backend/capellacollab/core/authentication/jwt_bearer.py b/backend/capellacollab/core/authentication/jwt_bearer.py
index 40dd2b523..b9b205d38 100644
--- a/backend/capellacollab/core/authentication/jwt_bearer.py
+++ b/backend/capellacollab/core/authentication/jwt_bearer.py
@@ -25,7 +25,7 @@ class JWTBearer(security.HTTPBearer):
     def __init__(self, auto_error: bool = True):
         super().__init__(auto_error=auto_error)
 
-    async def __call__(
+    async def __call__(  # type: ignore
         self, request: fastapi.Request
     ) -> dict[str, t.Any] | None:
         credentials: security.HTTPAuthorizationCredentials | None = (
diff --git a/backend/capellacollab/core/authentication/provider/azure/__main__.py b/backend/capellacollab/core/authentication/provider/azure/__main__.py
index dc70ee2db..6fc912111 100644
--- a/backend/capellacollab/core/authentication/provider/azure/__main__.py
+++ b/backend/capellacollab/core/authentication/provider/azure/__main__.py
@@ -1,6 +1,7 @@
 # SPDX-FileCopyrightText: Copyright DB Netz AG and the capella-collab-manager contributors
 # SPDX-License-Identifier: Apache-2.0
 
+import typing as t
 
 from capellacollab.config import config
 
@@ -13,8 +14,8 @@
 cfg = config["authentication"]["azure"]
 
 
-def get_jwk_cfg(token: str) -> dict[str, any]:
+def get_jwk_cfg(token: str) -> dict[str, t.Any]:
     return {
         "audience": cfg["client"]["id"],
-        "key": KeyStore.key_for_token(token).dict(),
+        "key": KeyStore.key_for_token(token).model_dump(),
     }
diff --git a/backend/capellacollab/core/authentication/provider/azure/keystore.py b/backend/capellacollab/core/authentication/provider/azure/keystore.py
index 65c400e17..a8945b565 100644
--- a/backend/capellacollab/core/authentication/provider/azure/keystore.py
+++ b/backend/capellacollab/core/authentication/provider/azure/keystore.py
@@ -12,11 +12,8 @@
 from jose import jwt
 
 from capellacollab.config import config
-from capellacollab.core.authentication.provider.models import (
-    InvalidTokenError,
-    JSONWebKeySet,
-    KeyIDNotFoundError,
-)
+
+from .. import models as provider_models
 
 log = logging.getLogger(__name__)
 cfg = config["authentication"]["azure"]
@@ -38,7 +35,7 @@ def __init__(
 
         self.jwks_uri = jwks_uri
         self.algorithms = algorithms
-        self.public_keys: dict[t.Any, t.Any] = {}
+        self.public_keys: dict[str, provider_models.JSONWebKey] = {}
         self.key_refresh_interval = key_refresh_interval
         self.public_keys_last_refreshed: float = 0
         self.refresh_keys()
@@ -56,7 +53,7 @@ def refresh_keys(self) -> None:
         except Exception:
             log.error("Could not retrieve JWKS data from %s", self.jwks_uri)
             return
-        jwks = JSONWebKeySet.parse_raw(resp.text)
+        jwks = provider_models.JSONWebKeySet.parse_raw(resp.text)
         self.public_keys_last_refreshed = time.time()
         self.public_keys.clear()
         for key in jwks.keys:
@@ -64,7 +61,7 @@ def refresh_keys(self) -> None:
 
     def key_for_token(
         self, token: str, *, in_retry: int = 0
-    ) -> dict[str, t.Any]:
+    ) -> provider_models.JSONWebKey:
         # Before we do anything, the validation keys may need to be refreshed.
         # If so, refresh them.
         if self.keys_need_refresh():
@@ -75,7 +72,9 @@ def key_for_token(
         try:
             unverified_claims = jwt.get_unverified_header(token)
         except Exception:
-            raise InvalidTokenError("Unable to parse key ID from token")
+            raise provider_models.InvalidTokenError(
+                "Unable to parse key ID from token"
+            )
 
         # See if we have the key identified by this key ID.
         try:
@@ -85,7 +84,7 @@ def key_for_token(
             # haven't refreshed keys yet), then try to refresh the keys and try
             # again.
             if in_retry:
-                raise KeyIDNotFoundError()
+                raise provider_models.KeyIDNotFoundError()
             self.refresh_keys()
             return self.key_for_token(token, in_retry=1)
 
diff --git a/backend/capellacollab/core/authentication/provider/azure/routes.py b/backend/capellacollab/core/authentication/provider/azure/routes.py
index aa055e458..6cf6b9abb 100644
--- a/backend/capellacollab/core/authentication/provider/azure/routes.py
+++ b/backend/capellacollab/core/authentication/provider/azure/routes.py
@@ -62,7 +62,10 @@ async def api_get_token(
     )
     access_token = token["id_token"]
 
-    username = get_username(JWTBearer().validate_token(access_token))
+    validated_token = JWTBearer().validate_token(access_token)
+    assert validated_token
+
+    username = get_username(validated_token)
 
     if user := users_crud.get_user_by_name(db, username):
         users_crud.update_last_login(db, user)
diff --git a/backend/capellacollab/core/authentication/provider/oauth/__main__.py b/backend/capellacollab/core/authentication/provider/oauth/__main__.py
index 3cbeefed8..803679fa3 100644
--- a/backend/capellacollab/core/authentication/provider/oauth/__main__.py
+++ b/backend/capellacollab/core/authentication/provider/oauth/__main__.py
@@ -15,5 +15,5 @@ def get_jwk_cfg(token: str) -> dict[str, t.Any]:
     return {
         "algorithms": ["RS256"],
         "audience": cfg["audience"] or cfg["client"]["id"],
-        "key": KeyStore.key_for_token(token).dict(),
+        "key": KeyStore.key_for_token(token).model_dump(),
     }
diff --git a/backend/capellacollab/core/authentication/provider/oauth/keystore.py b/backend/capellacollab/core/authentication/provider/oauth/keystore.py
index 9a01a680f..9480ced3c 100644
--- a/backend/capellacollab/core/authentication/provider/oauth/keystore.py
+++ b/backend/capellacollab/core/authentication/provider/oauth/keystore.py
@@ -14,6 +14,8 @@
 from capellacollab.config import config
 from capellacollab.core.authentication.provider import models
 
+from .. import models as provider_models
+
 log = logging.getLogger(__name__)
 cfg = config["authentication"]["oauth"]
 
@@ -35,7 +37,7 @@ def __init__(
         self.get_jwks_uri = get_jwks_uri
         self.jwks_uri = ""
         self.algorithms = algorithms
-        self.public_keys: dict[t.Any, t.Any] = {}
+        self.public_keys: dict[str, provider_models.JSONWebKey] = {}
         self.key_refresh_interval = key_refresh_interval
         self.public_keys_last_refreshed: float = 0
 
@@ -62,7 +64,7 @@ def refresh_keys(self) -> None:
 
     def key_for_token(
         self, token: str, *, in_retry: int = 0
-    ) -> dict[str, t.Any]:
+    ) -> provider_models.JSONWebKey:
         # Before we do anything, the validation keys may need to be refreshed.
         # If so, refresh them.
         if self.keys_need_refresh():
diff --git a/backend/capellacollab/core/authentication/provider/oauth/routes.py b/backend/capellacollab/core/authentication/provider/oauth/routes.py
index c368c6ec3..4f863b2fa 100644
--- a/backend/capellacollab/core/authentication/provider/oauth/routes.py
+++ b/backend/capellacollab/core/authentication/provider/oauth/routes.py
@@ -30,8 +30,12 @@ async def api_get_token(
     body: TokenRequest, db: orm.Session = fastapi.Depends(database.get_db)
 ):
     token = get_token(body.code)
+    access_token = token["id_token"]
 
-    username = get_username(JWTBearer().validate_token(token["access_token"]))
+    validated_token = JWTBearer().validate_token(access_token)
+    assert validated_token
+
+    username = get_username(validated_token)
 
     if user := users_crud.get_user_by_name(db, username):
         users_crud.update_last_login(db, user)
diff --git a/backend/capellacollab/core/database/__init__.py b/backend/capellacollab/core/database/__init__.py
index 7520238da..12d6a7b91 100644
--- a/backend/capellacollab/core/database/__init__.py
+++ b/backend/capellacollab/core/database/__init__.py
@@ -1,6 +1,7 @@
 # SPDX-FileCopyrightText: Copyright DB Netz AG and the capella-collab-manager contributors
 # SPDX-License-Identifier: Apache-2.0
 
+import typing as t
 
 import pydantic
 import sqlalchemy as sa
@@ -23,7 +24,7 @@ class Base(orm.DeclarativeBase):
 from . import models  # isort:skip # pylint: disable=unused-import
 
 
-def get_db() -> orm.Session:
+def get_db() -> t.Iterator[orm.Session]:
     with SessionLocal() as session:
         yield session
 
diff --git a/backend/capellacollab/core/database/migration.py b/backend/capellacollab/core/database/migration.py
index 4c6ed85f7..d3d78c1bd 100644
--- a/backend/capellacollab/core/database/migration.py
+++ b/backend/capellacollab/core/database/migration.py
@@ -162,6 +162,8 @@ def create_tools(db):
 
 def create_t4c_instance_and_repositories(db):
     tool = tools_crud.get_tool_by_name(db, "Capella")
+    assert tool
+
     version = tools_crud.get_version_by_tool_id_version_name(
         db, tool.id, "5.2.0"
     )
@@ -189,13 +191,17 @@ def create_t4c_instance_and_repositories(db):
 
 def create_models(db: orm.Session):
     capella_tool = tools_crud.get_tool_by_name(db, "Capella")
+    assert capella_tool
+
+    default_project = projects_crud.get_project_by_slug(db, "default")
+    assert default_project
 
     for version in ["5.0.0", "5.2.0", "6.0.0"]:
         capella_model = toolmodels_crud.create_model(
             db=db,
-            project=projects_crud.get_project_by_slug(db, "default"),
+            project=default_project,
             post_model=toolmodels_models.PostCapellaModel(
-                name=f"Meldody Model Test {version}",
+                name=f"Melody Model Test {version}",
                 description="",
                 tool_id=capella_tool.id,
             ),
diff --git a/backend/capellacollab/projects/routes.py b/backend/capellacollab/projects/routes.py
index ee78f1ee9..49a01f383 100644
--- a/backend/capellacollab/projects/routes.py
+++ b/backend/capellacollab/projects/routes.py
@@ -3,7 +3,6 @@
 
 
 import logging
-from collections import abc
 
 import fastapi
 import slugify
@@ -39,7 +38,7 @@
 )
 
 
-@router.get("", response_model=abc.Sequence[models.Project], tags=["Projects"])
+@router.get("", response_model=list[models.Project], tags=["Projects"])
 def get_projects(
     user: users_models.DatabaseUser = fastapi.Depends(
         users_injectables.get_own_user
@@ -49,18 +48,19 @@ def get_projects(
     log: logging.LoggerAdapter = fastapi.Depends(
         core_logging.get_request_logger
     ),
-) -> abc.Sequence[models.DatabaseProject]:
+) -> list[models.DatabaseProject]:
     if auth_injectables.RoleVerification(
         required_role=users_models.Role.ADMIN, verify=False
     )(token, db):
         log.debug("Fetching all projects")
-        return crud.get_projects(db)
+        return list(crud.get_projects(db))
 
     projects = [
         association.project
         for association in user.projects
         if not association.project.visibility == models.Visibility.INTERNAL
-    ] + crud.get_internal_projects(db)
+    ]
+    projects.extend(crud.get_internal_projects(db))
 
     log.debug("Fetching the following projects: %s", projects)
     return projects
@@ -89,7 +89,7 @@ def update_project(
     if crud.get_project_by_slug(db, new_slug) and project.slug != new_slug:
         raise fastapi.HTTPException(
             status_code=status.HTTP_409_CONFLICT,
-            details={
+            detail={
                 "reason": "A project with a similar name already exists.",
                 "technical": "Slug already used",
             },
@@ -137,7 +137,7 @@ def create_project(
     project = crud.create_project(
         db,
         post_project.name,
-        post_project.description,
+        post_project.description or "",
         post_project.visibility,
     )
 
diff --git a/backend/capellacollab/projects/toolmodels/backups/routes.py b/backend/capellacollab/projects/toolmodels/backups/routes.py
index 660c3531d..4db172b4b 100644
--- a/backend/capellacollab/projects/toolmodels/backups/routes.py
+++ b/backend/capellacollab/projects/toolmodels/backups/routes.py
@@ -29,6 +29,7 @@
 from capellacollab.tools import crud as tools_crud
 from capellacollab.users import models as users_models
 
+from .. import exceptions as toolmodels_exceptions
 from . import core, crud, exceptions, injectables, models
 from .runs import routes as runs_routes
 
@@ -100,6 +101,9 @@ def create_backup(
         )
 
     if body.run_nightly:
+        if not capella_model.version_id:
+            raise toolmodels_exceptions.VersionIdNotSetError(capella_model.id)
+
         reference = operators.get_operator().create_cronjob(
             image=tools_crud.get_backup_image_for_tool_version(
                 db, capella_model.version_id
diff --git a/backend/capellacollab/projects/toolmodels/backups/runs/interface.py b/backend/capellacollab/projects/toolmodels/backups/runs/interface.py
index 3ff14f7ca..1f227250d 100644
--- a/backend/capellacollab/projects/toolmodels/backups/runs/interface.py
+++ b/backend/capellacollab/projects/toolmodels/backups/runs/interface.py
@@ -12,6 +12,9 @@
 from capellacollab.config import config
 from capellacollab.core import database
 from capellacollab.core.logging import loki
+from capellacollab.projects.toolmodels import (
+    exceptions as toolmodels_exceptions,
+)
 from capellacollab.projects.toolmodels.backups import core as backups_core
 from capellacollab.sessions import operators
 from capellacollab.tools import crud as tools_crud
@@ -54,20 +57,21 @@ def _schedule_pending_jobs():
                 pending_run.pipeline.model.slug,
             )
             try:
+                model = pending_run.pipeline.model
+
+                if not model.version_id:
+                    raise toolmodels_exceptions.VersionIdNotSetError(model.id)
+
                 job_name = operators.get_operator().create_job(
                     image=tools_crud.get_backup_image_for_tool_version(
-                        db, pending_run.pipeline.model.version_id
+                        db, model.version_id
                     ),
                     command="backup",
                     labels={
-                        "app.capellacollab/projectSlug": pending_run.pipeline.model.project.slug,
-                        "app.capellacollab/projectID": str(
-                            pending_run.pipeline.model.project.id
-                        ),
-                        "app.capellacollab/modelSlug": pending_run.pipeline.model.slug,
-                        "app.capellacollab/modelID": str(
-                            pending_run.pipeline.model.id
-                        ),
+                        "app.capellacollab/projectSlug": model.project.slug,
+                        "app.capellacollab/projectID": str(model.project.id),
+                        "app.capellacollab/modelSlug": model.slug,
+                        "app.capellacollab/modelID": str(model.id),
                         "app.capellacollab/pipelineID": str(
                             pending_run.pipeline.id
                         ),
diff --git a/backend/capellacollab/projects/toolmodels/backups/validation.py b/backend/capellacollab/projects/toolmodels/backups/validation.py
index 0f1034683..ae1d0c40f 100644
--- a/backend/capellacollab/projects/toolmodels/backups/validation.py
+++ b/backend/capellacollab/projects/toolmodels/backups/validation.py
@@ -11,7 +11,7 @@
 
 def check_last_pipeline_run_status(
     db: orm.Session, model: toolmodel_models.DatabaseCapellaModel
-) -> runs_models.PipelineRunStatus:
+) -> runs_models.PipelineRunStatus | None:
     if pipeline := crud.get_first_pipeline_for_tool_model(db, model):
         # Only consider first pipeline for monitoring, usually there is only one pipeline.
         if pipeline_run := runs_crud.get_last_pipeline_run_of_pipeline(
diff --git a/backend/capellacollab/projects/toolmodels/diagrams/models.py b/backend/capellacollab/projects/toolmodels/diagrams/models.py
index c17d8943a..7ab752382 100644
--- a/backend/capellacollab/projects/toolmodels/diagrams/models.py
+++ b/backend/capellacollab/projects/toolmodels/diagrams/models.py
@@ -10,16 +10,12 @@
 
 
 class DiagramMetadata(pydantic.BaseModel):
-    model_config = pydantic.ConfigDict(from_attributes=True)
-
     name: str
     uuid: str
     success: bool
 
 
 class DiagramCacheMetadata(pydantic.BaseModel):
-    model_config = pydantic.ConfigDict(from_attributes=True)
-
     diagrams: list[DiagramMetadata]
     last_updated: datetime.datetime
 
diff --git a/backend/capellacollab/projects/toolmodels/diagrams/routes.py b/backend/capellacollab/projects/toolmodels/diagrams/routes.py
index 835516306..148cd6aec 100644
--- a/backend/capellacollab/projects/toolmodels/diagrams/routes.py
+++ b/backend/capellacollab/projects/toolmodels/diagrams/routes.py
@@ -40,7 +40,7 @@ async def get_diagram_metadata(
     try:
         (
             last_updated,
-            diagrams,
+            diagram_metadata_entries,
         ) = await handler.get_file_from_repository_or_artifacts_as_json(
             "diagram_cache/index.json",
             "update_capella_diagram_cache",
@@ -57,8 +57,13 @@ async def get_diagram_metadata(
                 ),
             },
         )
+
     return models.DiagramCacheMetadata(
-        diagrams=diagrams, last_updated=last_updated
+        diagrams=[
+            models.DiagramMetadata.model_validate(diagram_metadata)
+            for diagram_metadata in diagram_metadata_entries
+        ],
+        last_updated=last_updated,
     )
 
 
diff --git a/backend/capellacollab/projects/toolmodels/exceptions.py b/backend/capellacollab/projects/toolmodels/exceptions.py
new file mode 100644
index 000000000..f07233e60
--- /dev/null
+++ b/backend/capellacollab/projects/toolmodels/exceptions.py
@@ -0,0 +1,30 @@
+# SPDX-FileCopyrightText: Copyright DB Netz AG and the capella-collab-manager contributors
+# SPDX-License-Identifier: Apache-2.0
+
+import fastapi
+from fastapi import exception_handlers, status
+
+
+class VersionIdNotSetError(Exception):
+    def __init__(self, toolmodel_id: int):
+        self.toolmodel_id = toolmodel_id
+
+
+async def version_id_not_set_exception_handler(
+    request: fastapi.Request, exc: VersionIdNotSetError
+) -> fastapi.Response:
+    return await exception_handlers.http_exception_handler(
+        request,
+        fastapi.HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail={
+                "reason": f"The toolmodel with id {exc.toolmodel_id} does not have a version set."
+            },
+        ),
+    )
+
+
+def register_exceptions(app: fastapi.FastAPI):
+    app.add_exception_handler(
+        VersionIdNotSetError, version_id_not_set_exception_handler
+    )
diff --git a/backend/capellacollab/projects/toolmodels/modelsources/git/exceptions.py b/backend/capellacollab/projects/toolmodels/modelsources/git/exceptions.py
index 906d24ebf..0837c0513 100644
--- a/backend/capellacollab/projects/toolmodels/modelsources/git/exceptions.py
+++ b/backend/capellacollab/projects/toolmodels/modelsources/git/exceptions.py
@@ -34,6 +34,12 @@ class GitPipelineJobFailedError(Exception):
     job_name: str
 
 
+@dataclasses.dataclass
+class GitPipelineJobUnknownStateError(Exception):
+    job_name: str
+    state: str
+
+
 class GithubArtifactExpiredError(Exception):
     pass
 
@@ -110,6 +116,24 @@ async def git_pipeline_job_failed_handler(
     )
 
 
+async def unknown_state_handler(
+    request: fastapi.Request, exc: GitPipelineJobUnknownStateError
+) -> fastapi.Response:
+    return await exception_handlers.http_exception_handler(
+        request,
+        fastapi.HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail={
+                "err_code": "UNKNOWN_STATE_ERROR",
+                "reason": (
+                    f"Job '{exc.job_name}' has an unhandled or unknown state: '{exc.state}'",
+                    "Please contact your administrator.",
+                ),
+            },
+        ),
+    )
+
+
 async def github_artifact_expired_handler(
     request: fastapi.Request, _: GithubArtifactExpiredError
 ) -> fastapi.Response:
@@ -141,6 +165,9 @@ def register_exceptions(app: fastapi.FastAPI):
         GitPipelineJobNotFoundError,
         git_pipeline_job_not_found_handler,
     )
+    app.add_exception_handler(
+        GitPipelineJobUnknownStateError, unknown_state_handler
+    )
     app.add_exception_handler(
         GitPipelineJobFailedError,
         git_pipeline_job_failed_handler,
diff --git a/backend/capellacollab/projects/toolmodels/modelsources/git/github/handler.py b/backend/capellacollab/projects/toolmodels/modelsources/git/github/handler.py
index 37b2c0cb3..77fce82fd 100644
--- a/backend/capellacollab/projects/toolmodels/modelsources/git/github/handler.py
+++ b/backend/capellacollab/projects/toolmodels/modelsources/git/github/handler.py
@@ -61,7 +61,7 @@ def __get_file_from_repository(
         self,
         project_id: str,
         trusted_file_path: str,
-        revision: str | None = None,
+        revision: str,
         headers: dict[str, str] | None = None,
     ) -> requests.Response:
         return requests.get(
@@ -179,7 +179,9 @@ def __get_latest_successful_job(self, jobs: list, job_name: str) -> dict:
         ):
             raise git_exceptions.GitPipelineJobFailedError(job_name)
 
-        return None
+        raise git_exceptions.GitPipelineJobUnknownStateError(
+            job_name, matched_jobs[0]["conclusion"]
+        )
 
     def __get_latest_artifact_metadata(self, project_id: str, job_id: str):
         response = requests.get(
diff --git a/backend/capellacollab/projects/toolmodels/modelsources/git/handler/factory.py b/backend/capellacollab/projects/toolmodels/modelsources/git/handler/factory.py
index d52620a25..3ef107284 100644
--- a/backend/capellacollab/projects/toolmodels/modelsources/git/handler/factory.py
+++ b/backend/capellacollab/projects/toolmodels/modelsources/git/handler/factory.py
@@ -28,7 +28,7 @@ def create_git_handler(
                 return github_handler.GithubHandler(git_model, git_instance)
             case _:
                 raise exceptions.GitInstanceUnsupportedError(
-                    instance_name=git_instance.type
+                    instance_name=str(git_instance.type)
                 )
 
     @staticmethod
diff --git a/backend/capellacollab/projects/toolmodels/modelsources/git/handler/handler.py b/backend/capellacollab/projects/toolmodels/modelsources/git/handler/handler.py
index 75ebe750c..06f9ac632 100644
--- a/backend/capellacollab/projects/toolmodels/modelsources/git/handler/handler.py
+++ b/backend/capellacollab/projects/toolmodels/modelsources/git/handler/handler.py
@@ -7,6 +7,7 @@
 import typing as t
 
 import requests
+from capellambse import diagram_cache
 
 import capellacollab.projects.toolmodels.modelsources.git.models as git_models
 import capellacollab.settings.modelsources.git.models as settings_git_models
@@ -34,7 +35,7 @@ async def get_project_id_by_git_url(self) -> str:
 
     @abc.abstractmethod
     async def get_last_job_run_id_for_git_model(
-        self, job_name: str, project_id: str | None
+        self, job_name: str, project_id: str | None = None
     ) -> tuple[str, str]:
         pass
 
@@ -76,7 +77,7 @@ async def get_file_from_repository_or_artifacts_as_json(
         trusted_file_path: str,
         job_name: str,
         revision: str | None = None,
-    ) -> tuple[datetime.datetime, dict[str, t.Any]]:
+    ) -> tuple[datetime.datetime, list[diagram_cache.IndexEntry]]:
         (
             last_updated,
             result,
diff --git a/backend/capellacollab/projects/users/routes.py b/backend/capellacollab/projects/users/routes.py
index 08560add3..c12e7d56f 100644
--- a/backend/capellacollab/projects/users/routes.py
+++ b/backend/capellacollab/projects/users/routes.py
@@ -60,7 +60,7 @@ def get_project_user_association_or_raise(
         return models.ProjectUser(
             role=models.ProjectUserRole.USER,
             permission=models.ProjectUserPermission.READ,
-            user=user,
+            user=users_models.User.model_validate(user),
         )
 
     raise fastapi.HTTPException(
@@ -88,7 +88,7 @@ def get_current_user(
         return models.ProjectUser(
             role=models.ProjectUserRole.ADMIN,
             permission=models.ProjectUserPermission.WRITE,
-            user=user,
+            user=users_models.User.model_validate(user),
         )
     return get_project_user_association_or_raise(db, project, user)
 
diff --git a/backend/capellacollab/sessions/files/routes.py b/backend/capellacollab/sessions/files/routes.py
index 41fc4a20d..a0c6709cc 100644
--- a/backend/capellacollab/sessions/files/routes.py
+++ b/backend/capellacollab/sessions/files/routes.py
@@ -63,6 +63,8 @@ def upload_files(
 
         for file in files:
             file.file.seek(0)
+
+            assert file.filename
             file.filename = file.filename.replace(" ", "_")
             tar.addfile(
                 tar.gettarinfo(arcname=file.filename, fileobj=file.file),
diff --git a/backend/capellacollab/sessions/hooks/jupyter.py b/backend/capellacollab/sessions/hooks/jupyter.py
index 78dd23d11..3bc359b2d 100644
--- a/backend/capellacollab/sessions/hooks/jupyter.py
+++ b/backend/capellacollab/sessions/hooks/jupyter.py
@@ -41,7 +41,7 @@ def __init__(self):
         )
         self._general_conf = config["general"]
 
-    def configuration_hook(
+    def configuration_hook(  # type: ignore[override]
         self,
         db: orm.Session,
         user: users_models.DatabaseUser,
@@ -65,7 +65,7 @@ def configuration_hook(
 
         volumes = self._get_project_share_volume_mounts(db, token, tool)
 
-        return environment, volumes, []
+        return environment, volumes, []  # type: ignore[return-value]
 
     def post_session_creation_hook(
         self,
@@ -76,12 +76,12 @@ def post_session_creation_hook(
     ):
         operator.create_public_route(
             session_id=session_id,
-            host=self._jupyter_public_uri.hostname,
+            host=self._jupyter_public_uri.hostname or "",
             path=self._determine_base_url(user.name),
             port=8888,
         )
 
-    def pre_session_termination_hook(
+    def pre_session_termination_hook(  # type: ignore
         self,
         operator: operators.KubernetesOperator,
         session: sessions_models.DatabaseSession,
diff --git a/backend/capellacollab/sessions/hooks/persistent_workspace.py b/backend/capellacollab/sessions/hooks/persistent_workspace.py
index a54f120bb..6613c04b3 100644
--- a/backend/capellacollab/sessions/hooks/persistent_workspace.py
+++ b/backend/capellacollab/sessions/hooks/persistent_workspace.py
@@ -22,7 +22,7 @@ class PersistentWorkspaceHook(interface.HookRegistration):
     Is responsible for mounting the persistent workspace into persistent sessions.
     """
 
-    def configuration_hook(
+    def configuration_hook(  # type: ignore
         self,
         operator: operators.KubernetesOperator,
         user: users_models.DatabaseUser,
diff --git a/backend/capellacollab/sessions/hooks/pure_variants.py b/backend/capellacollab/sessions/hooks/pure_variants.py
index e5d648598..1a02d40f9 100644
--- a/backend/capellacollab/sessions/hooks/pure_variants.py
+++ b/backend/capellacollab/sessions/hooks/pure_variants.py
@@ -25,7 +25,7 @@ class PureVariantsConfigEnvironment(t.TypedDict):
 
 
 class PureVariantsIntegration(interface.HookRegistration):
-    def configuration_hook(
+    def configuration_hook(  # type: ignore
         self,
         db: orm.Session,
         user: users_models.DatabaseUser,
diff --git a/backend/capellacollab/sessions/hooks/t4c.py b/backend/capellacollab/sessions/hooks/t4c.py
index 03011f775..ce094b858 100644
--- a/backend/capellacollab/sessions/hooks/t4c.py
+++ b/backend/capellacollab/sessions/hooks/t4c.py
@@ -35,7 +35,7 @@ class T4CConfigEnvironment(t.TypedDict):
 
 
 class T4CIntegration(interface.HookRegistration):
-    def configuration_hook(
+    def configuration_hook(  # type: ignore
         self,
         db: orm.Session,
         user: users_models.DatabaseUser,
@@ -47,7 +47,6 @@ def configuration_hook(
         list[operators_models.Volume],
         list[core_models.Message],
     ]:
-        environment = {}
         warnings: list[core_models.Message] = []
 
         # When using a different tool with TeamForCapella support (e.g., Capella + pure::variants),
@@ -57,7 +56,7 @@ def configuration_hook(
             db, tool_version.name, user
         )
 
-        environment["T4C_JSON"] = json.dumps(
+        t4c_json = json.dumps(
             [
                 {
                     "repository": repository.name,
@@ -72,12 +71,16 @@ def configuration_hook(
             ]
         )
 
-        environment["T4C_LICENCE_SECRET"] = (
-            t4c_repositories[0].instance.license if t4c_repositories else None
+        t4c_licence_secret = (
+            t4c_repositories[0].instance.license if t4c_repositories else ""
         )
 
-        environment["T4C_USERNAME"] = user.name
-        environment["T4C_PASSWORD"] = credentials.generate_password()
+        environment = T4CConfigEnvironment(
+            T4C_LICENCE_SECRET=t4c_licence_secret,
+            T4C_JSON=t4c_json,
+            T4C_USERNAME=user.name,
+            T4C_PASSWORD=credentials.generate_password(),
+        )
 
         for repository in t4c_repositories:
             try:
@@ -109,7 +112,7 @@ def configuration_hook(
 
         return environment, [], warnings
 
-    def pre_session_termination_hook(
+    def pre_session_termination_hook(  # type: ignore
         self,
         db: orm.Session,
         session: sessions_models.DatabaseSession,
diff --git a/backend/capellacollab/sessions/models.py b/backend/capellacollab/sessions/models.py
index 5413f9ce4..c8088bcc3 100644
--- a/backend/capellacollab/sessions/models.py
+++ b/backend/capellacollab/sessions/models.py
@@ -29,18 +29,17 @@ class WorkspaceType(enum.Enum):
     READONLY = "readonly"
 
 
-class GetSessionsResponse(pydantic.BaseModel):
+class Session(pydantic.BaseModel):
     model_config = pydantic.ConfigDict(from_attributes=True)
 
     id: str
     type: WorkspaceType
     created_at: datetime.datetime
     owner: users_models.BaseUser
-    state: str
+
     guacamole_username: str | None = None
     guacamole_connection_id: str | None = None
-    warnings: list[core_models.Message] | None = None
-    last_seen: str
+
     project: projects_models.Project | None = None
     version: tools_models.ToolVersionWithTool | None = None
 
@@ -49,7 +48,11 @@ class GetSessionsResponse(pydantic.BaseModel):
     )
 
 
-class OwnSessionResponse(GetSessionsResponse):
+class GetSessionsResponse(Session):
+    state: str
+    warnings: list[core_models.Message] | None = None
+    last_seen: str
+
     t4c_password: str | None = None
     jupyter_uri: str | None = None
 
diff --git a/backend/capellacollab/sessions/operators/k8s.py b/backend/capellacollab/sessions/operators/k8s.py
index 439204cd2..8b664e5c3 100644
--- a/backend/capellacollab/sessions/operators/k8s.py
+++ b/backend/capellacollab/sessions/operators/k8s.py
@@ -150,7 +150,7 @@ def start_session(
         session_type: str,
         tool_name: str,
         version_name: str,
-        environment: dict[str, str | None],
+        environment: dict[str, str],
         ports: dict[str, int],
         volumes: list[models.Volume],
         prometheus_path="/metrics",
@@ -441,7 +441,7 @@ def _create_deployment(
         self,
         image: str,
         name: str,
-        environment: dict[str, str | None],
+        environment: dict[str, str],
         ports: dict[str, int],
         volumes: list[models.Volume],
         limits: str = "high",
@@ -745,7 +745,7 @@ def _create_openshift_route(
         return v1_routes.create(body=route_dict, namespace=namespace)
 
     def create_persistent_volume(
-        self, name: str, size: str, labels: dict[str, str] = None
+        self, name: str, size: str, labels: dict[str, str] | None = None
     ):
         pvc: client.V1PersistentVolumeClaim = client.V1PersistentVolumeClaim(
             kind="PersistentVolumeClaim",
@@ -950,7 +950,7 @@ def print_file_tree_as_json():
 
             print("Using CLI arguments: " + str(sys.argv[1:]), file=sys.stderr)
 
-            def get_files(dir: pathlib.PosixPath, show_hidden: bool):
+            def get_files(dir: pathlib.Path, show_hidden: bool):
                 file = {
                     "path": str(dir.absolute()),
                     "name": dir.name,
diff --git a/backend/capellacollab/sessions/routes.py b/backend/capellacollab/sessions/routes.py
index 36aa16e81..8021ae91f 100644
--- a/backend/capellacollab/sessions/routes.py
+++ b/backend/capellacollab/sessions/routes.py
@@ -263,7 +263,7 @@ def models_as_json(
 def git_model_as_json(
     git_model: git_models.DatabaseGitModel, deep_clone: bool
 ) -> dict[str, str | int]:
-    d = {
+    d: dict[str, str | int] = {
         "url": git_model.path,
         "revision": git_model.revision,
         "depth": 0 if deep_clone else 1,
@@ -474,21 +474,27 @@ def create_database_session(
     version: tools_models.DatabaseVersion,
     project: projects_models.DatabaseProject | None,
     **kwargs,
-) -> models.DatabaseSession:
-    database_model = models.DatabaseSession(
-        tool=tool,
-        version=version,
-        owner_name=owner,
-        project=project,
-        type=type,
-        **session,
-        **kwargs,
+) -> models.GetSessionsResponse:
+    db_session = crud.create_session(
+        db,
+        models.DatabaseSession(
+            tool=tool,
+            version=version,
+            owner_name=owner,
+            project=project,
+            type=type,
+            **session,
+            **kwargs,
+        ),
     )
-    response = crud.create_session(db=db, session=database_model)
-    response.state = "New"
-    response.last_seen = "UNKNOWN"
-    response.warnings = []
-    return response
+
+    session_dict = models.Session.model_validate(db_session).model_dump()
+
+    session_dict["state"] = "New"
+    session_dict["last_seen"] = "UNKNOWN"
+    session_dict["warnings"] = []
+
+    return models.GetSessionsResponse.model_validate(session_dict)
 
 
 def create_database_and_guacamole_session(
@@ -501,7 +507,7 @@ def create_database_and_guacamole_session(
     version: tools_models.DatabaseVersion,
     project: projects_models.DatabaseProject | None,
     environment: dict[str, str],
-) -> models.DatabaseSession:
+) -> models.GetSessionsResponse:
     guacamole_username = credentials.generate_password()
     guacamole_password = credentials.generate_password(length=64)
 
@@ -568,6 +574,14 @@ def create_guacamole_token(
             },
         )
 
+    if not (session.guacamole_username and session.guacamole_password):
+        raise fastapi.HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail={
+                "reason": "The session does not contain a guacamole username or password"
+            },
+        )
+
     token = guacamole.get_token(
         session.guacamole_username, session.guacamole_password
     )
@@ -581,7 +595,7 @@ def create_guacamole_token(
 
 
 @users_router.get(
-    "/{user_id}/sessions", response_model=list[models.OwnSessionResponse]
+    "/{user_id}/sessions", response_model=list[models.GetSessionsResponse]
 )
 def get_sessions_for_user(
     user: users_models.DatabaseUser = fastapi.Depends(
diff --git a/backend/capellacollab/sessions/sessions.py b/backend/capellacollab/sessions/sessions.py
index e1775dddd..b58130da1 100644
--- a/backend/capellacollab/sessions/sessions.py
+++ b/backend/capellacollab/sessions/sessions.py
@@ -1,10 +1,9 @@
 # SPDX-FileCopyrightText: Copyright DB Netz AG and the capella-collab-manager contributors
 # SPDX-License-Identifier: Apache-2.0
 
-
 import logging
 import re
-import typing as t
+from collections import abc
 
 import requests
 
@@ -16,15 +15,26 @@
 
 
 def inject_attrs_in_sessions(
-    db_sessions: list[models.DatabaseSession],
-) -> list[dict[str, t.Any]]:
+    db_sessions: abc.Sequence[models.DatabaseSession],
+) -> list[models.GetSessionsResponse]:
     sessions_list = []
     for session in db_sessions:
-        session.state = _determine_session_state(session)
-        session.last_seen = get_last_seen(session.id)
-        session.jupyter_uri = session.environment.get("JUPYTER_URI")
-        session.t4c_password = session.environment.get("T4C_PASSWORD")
-        sessions_list.append(session)
+        session_dict = models.Session.model_validate(session).model_dump()
+
+        session_dict["state"] = _determine_session_state(session)
+        session_dict["last_seen"] = get_last_seen(session.id)
+
+        if session.environment:
+            session_dict["jupyter_uri"] = session.environment.get(
+                "JUPYTER_URI"
+            )
+            session_dict["t4c_password"] = session.environment.get(
+                "T4C_PASSWORD"
+            )
+
+        sessions_list.append(
+            models.GetSessionsResponse.model_validate(session_dict)
+        )
 
     return sessions_list
 
diff --git a/backend/capellacollab/settings/integrations/purevariants/crud.py b/backend/capellacollab/settings/integrations/purevariants/crud.py
index 06d7964db..85fcb0d54 100644
--- a/backend/capellacollab/settings/integrations/purevariants/crud.py
+++ b/backend/capellacollab/settings/integrations/purevariants/crud.py
@@ -17,7 +17,7 @@ def get_pure_variants_configuration(
 
 
 def set_license_server_configuration(
-    db: orm.Session, value: str
+    db: orm.Session, value: str | None
 ) -> models.DatabasePureVariantsLicenses:
     if pv_license := get_pure_variants_configuration(db):
         pv_license.license_server_url = value
diff --git a/backend/capellacollab/tools/models.py b/backend/capellacollab/tools/models.py
index c5eee635f..d503de71c 100644
--- a/backend/capellacollab/tools/models.py
+++ b/backend/capellacollab/tools/models.py
@@ -22,7 +22,7 @@ class DatabaseTool(database.Base):
 
     id: orm.Mapped[int] = orm.mapped_column(primary_key=True)
 
-    name: orm.Mapped[str | None]
+    name: orm.Mapped[str]
     docker_image_template: orm.Mapped[str]
     docker_image_backup_template: orm.Mapped[str | None]
     readonly_docker_image_template: orm.Mapped[str | None]
diff --git a/backend/capellacollab/tools/routes.py b/backend/capellacollab/tools/routes.py
index 7d686d9d3..c36d12e8e 100644
--- a/backend/capellacollab/tools/routes.py
+++ b/backend/capellacollab/tools/routes.py
@@ -282,7 +282,12 @@ def raise_when_tool_dependency_exist(
         for model in tool_models
     )
 
-    raise_if_dependencies_exist(dependencies, tool.name, "tool")
+    if dependencies:
+        raise core_exceptions.ExistingDependenciesError(
+            entity_name=tool.name,
+            entity_type="tool",
+            dependencies=dependencies,
+        )
 
 
 def raise_when_tool_version_dependency_exist(
@@ -314,11 +319,12 @@ def raise_when_tool_version_dependency_exist(
         for model in version_models
     )
 
-    raise core_exceptions.ExistingDependenciesError(
-        entity_name=version.name,
-        entity_type="version",
-        dependencies=dependencies,
-    )
+    if dependencies:
+        raise core_exceptions.ExistingDependenciesError(
+            entity_name=version.name,
+            entity_type="version",
+            dependencies=dependencies,
+        )
 
 
 def raise_when_tool_nature_dependency_exist(
@@ -341,8 +347,9 @@ def raise_when_tool_nature_dependency_exist(
         for model in nature_models
     )
 
-    raise core_exceptions.ExistingDependenciesError(
-        entity_name=nature.name,
-        entity_type="nature",
-        dependencies=dependencies,
-    )
+    if dependencies:
+        raise core_exceptions.ExistingDependenciesError(
+            entity_name=nature.name,
+            entity_type="nature",
+            dependencies=dependencies,
+        )
diff --git a/backend/pyproject.toml b/backend/pyproject.toml
index f165432c8..7d24ea5b9 100644
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@@ -27,6 +27,7 @@ dependencies = [
   "alembic==1.10.4",
   "appdirs",
   "cachetools",
+  "capellambse==0.5.35.dev4",
   "fastapi>=0.101.0",
   "kubernetes",
   "msal",
@@ -100,6 +101,7 @@ show_error_codes = true
 warn_redundant_casts = true
 warn_unreachable = true
 python_version = "3.11"
+exclude = "capellacollab/alembic"
 
 [[tool.mypy.overrides]]
 module = ["tests.*"]
@@ -109,7 +111,26 @@ allow_untyped_defs = true
 [[tool.mypy.overrides]]
 # Untyped third party libraries
 module = [
-  # ...
+  "capellambse.*",
+  "kubernetes.*",
+  "prometheus_client.*",
+  "openshift.*",
+  "deepdiff.*",
+  "appdirs.*",
+  "jsonschema.*",
+  "requests.*",
+  "jose.*",
+  "slugify.*",
+  "cachetools.*",
+  "requests_oauthlib.*",
+  "msal.*",
+  "yaml.*",
+  "fastapi_pagination.*",
+  "aiohttp.*",
+  "starlette_prometheus.*",
+  "uvicorn.*",
+  "alembic.*",
+  "jwt.*",
 ]
 ignore_missing_imports = true