diff --git a/.build.yml b/.build.yml
index 0297938..f6c79c7 100644
--- a/.build.yml
+++ b/.build.yml
@@ -5,7 +5,15 @@ environment:
   NIX_CONFIG: "experimental-features = nix-command flakes"
 shell: true
 tasks:
-  - setup: |
+  - check format: |
       cd triviOS
-  - build: |
-      nix build ./triviOS\#nixosConfigurations.triviOS.config.system.build.toplevel --print-build-logs
+      nix fmt
+      git diff-index --quiet HEAD --
+      diff=$?
+
+      if [ "$diff" -eq 1 ]; then
+          echo "Invalid format."
+          exit 1
+      else
+          echo "Done."
+      fi