diff --git a/l4d2web/alembic/script.py.mako b/l4d2web/alembic/script.py.mako
new file mode 100644
index 0000000..1101630
--- /dev/null
+++ b/l4d2web/alembic/script.py.mako
@@ -0,0 +1,28 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[str], None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    ${downgrades if downgrades else "pass"}
diff --git a/l4d2web/alembic/versions/b2c684fddbd3_make_server_port_unique.py b/l4d2web/alembic/versions/b2c684fddbd3_make_server_port_unique.py
new file mode 100644
index 0000000..4d961f1
--- /dev/null
+++ b/l4d2web/alembic/versions/b2c684fddbd3_make_server_port_unique.py
@@ -0,0 +1,32 @@
+"""make server port unique
+
+Revision ID: b2c684fddbd3
+Revises: 0001_initial
+Create Date: 2026-05-06 20:52:35.109176
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'b2c684fddbd3'
+down_revision: Union[str, Sequence[str], None] = '0001_initial'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_unique_constraint(None, 'servers', ['port'])
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_constraint(None, 'servers', type_='unique')
+    # ### end Alembic commands ###
diff --git a/l4d2web/models.py b/l4d2web/models.py
index dd6fa0d..2070573 100644
--- a/l4d2web/models.py
+++ b/l4d2web/models.py
@@ -63,7 +63,7 @@ class Server(Base):
     user_id: Mapped[int] = mapped_column(ForeignKey("users.id"), nullable=False)
     blueprint_id: Mapped[int] = mapped_column(ForeignKey("blueprints.id"), nullable=False)
     name: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
-    port: Mapped[int] = mapped_column(Integer, nullable=False)
+    port: Mapped[int] = mapped_column(Integer, unique=True, nullable=False)
     desired_state: Mapped[str] = mapped_column(String(16), default="stopped", nullable=False)
     actual_state: Mapped[str] = mapped_column(String(16), default="unknown", nullable=False)
     actual_state_updated_at: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)
diff --git a/l4d2web/routes/server_routes.py b/l4d2web/routes/server_routes.py
index 89e6e33..e691397 100644
--- a/l4d2web/routes/server_routes.py
+++ b/l4d2web/routes/server_routes.py
@@ -1,5 +1,6 @@
 from flask import Blueprint, Response, jsonify, redirect, request
 from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
 
 from l4d2web.auth import current_user, require_login
 from l4d2web.db import session_scope
@@ -38,7 +39,13 @@ def create_server() -> Response:
             last_error="",
         )
         db.add(server)
-        db.flush()
+        
+        try:
+            db.flush()
+        except IntegrityError:
+            db.rollback()
+            return Response("port already in use", status=409)
+            
         server_id = server.id
 
     if json_response: