diff --git a/src/database/setups.py b/src/database/setups.py
new file mode 100644
index 00000000..6ac0c83f
--- /dev/null
+++ b/src/database/setups.py
@@ -0,0 +1,49 @@
+from sqlalchemy import Connection, text
+from sqlalchemy.engine import Row
+
+
+def get(id_: int, connection: Connection) -> Row | None:
+    """Get the setup by its ID."""
+    row = connection.execute(
+        text(
+            """
+            SELECT *
+            FROM algorithm_setup
+            WHERE sid = :setup_id
+            """,
+        ),
+        parameters={"setup_id": id_},
+    )
+    return row.one_or_none()
+
+
+def get_tags_for(id_: int, connection: Connection) -> list[str]:
+    """Get all tags for a specific setup."""
+    rows = connection.execute(
+        text(
+            """
+            SELECT tag
+            FROM setup_tag
+            WHERE id = :setup_id
+            """,
+        ),
+        parameters={"setup_id": id_},
+    )
+    return [row.tag for row in rows]
+
+
+def tag(id_: int, tag_: str, *, user_id: int, connection: Connection) -> None:
+    """Insert a new tag for the setup."""
+    connection.execute(
+        text(
+            """
+            INSERT INTO setup_tag(`id`, `tag`, `uploader`)
+            VALUES (:setup_id, :tag, :user_id)
+            """,
+        ),
+        parameters={
+            "setup_id": id_,
+            "user_id": user_id,
+            "tag": tag_,
+        },
+    )
diff --git a/src/main.py b/src/main.py
index 560b4c50..dca6fc73 100644
--- a/src/main.py
+++ b/src/main.py
@@ -11,6 +11,7 @@
 from routers.openml.evaluations import router as evaluationmeasures_router
 from routers.openml.flows import router as flows_router
 from routers.openml.qualities import router as qualities_router
+from routers.openml.setups import router as setups_router
 from routers.openml.study import router as study_router
 from routers.openml.tasks import router as task_router
 from routers.openml.tasktype import router as ttype_router
@@ -47,6 +48,7 @@ def create_api() -> FastAPI:
     app = FastAPI(**fastapi_kwargs)
 
     app.include_router(datasets_router)
+    app.include_router(setups_router)
     app.include_router(qualities_router)
     app.include_router(mldcat_ap_router)
     app.include_router(ttype_router)
diff --git a/src/routers/openml/setups.py b/src/routers/openml/setups.py
new file mode 100644
index 00000000..8af937cf
--- /dev/null
+++ b/src/routers/openml/setups.py
@@ -0,0 +1,68 @@
+from http import HTTPStatus
+from typing import Annotated, Any
+
+from fastapi import APIRouter, Body, Depends, HTTPException
+from sqlalchemy import Connection
+
+import database.setups
+from database.users import User, UserGroup
+from routers.dependencies import expdb_connection, fetch_user
+from routers.types import SystemString64
+
+router = APIRouter(prefix="/setup", tags=["setups"])
+
+
+def create_authentication_failed_error() -> HTTPException:
+    return HTTPException(
+        status_code=HTTPStatus.PRECONDITION_FAILED,
+        detail={"code": "103", "message": "Authentication failed"},
+    )
+
+
+def create_tag_exists_error(setup_id: int, tag: str) -> HTTPException:
+    return HTTPException(
+        # Changed from INTERNAL_SERVER_ERROR (500) to CONFLICT (409)
+        status_code=HTTPStatus.CONFLICT,
+        detail={
+            "code": "473",
+            "message": "Entity already tagged by this tag.",
+            "additional_information": f"id={setup_id}; tag={tag}",
+        },
+    )
+
+
+@router.post("/tag")
+def tag_setup(
+    setup_id: Annotated[int, Body()],
+    tag: Annotated[str, Body(..., embed=False), SystemString64],
+    user: Annotated[User | None, Depends(fetch_user)] = None,
+    expdb_db: Annotated[Connection, Depends(expdb_connection)] = None,
+) -> dict[str, dict[str, Any]]:
+    # 1. AUTHENTICATE FIRST
+    if user is None:
+        raise create_authentication_failed_error()
+
+    # 2. VERIFY EXISTENCE
+    setup = database.setups.get(setup_id, expdb_db)
+    if not setup:
+        raise HTTPException(status_code=HTTPStatus.NOT_FOUND, detail="Setup not found")
+
+    # 3. VERIFY OWNERSHIP / PERMISSIONS
+    # (Fixes the crash by not looking for a Dataset 'visibility' column)
+    is_admin = UserGroup.ADMIN in user.groups
+    is_owner = getattr(setup, "uploader", None) == user.user_id
+
+    if not (is_admin or is_owner):
+        raise HTTPException(status_code=HTTPStatus.FORBIDDEN, detail="No access granted")
+
+    # 4. CHECK IF TAG EXISTS
+    tags = database.setups.get_tags_for(setup_id, expdb_db)
+    if tag.casefold() in [t.casefold() for t in tags]:
+        raise create_tag_exists_error(setup_id, tag)
+
+    # 5. APPLY THE TAG
+    database.setups.tag(setup_id, tag, user_id=user.user_id, connection=expdb_db)
+
+    return {
+        "setup_tag": {"id": str(setup_id), "tag": [*tags, tag]},
+    }