diff --git a/.woodpecker.yaml b/.woodpecker.yaml
index 2f4d6d2..727a9a4 100644
--- a/.woodpecker.yaml
+++ b/.woodpecker.yaml
@@ -1,4 +1,16 @@
 steps:
+  - name: HTML syntax check
+    image: debian:12
+    # Debian has tidy 5.6.0, which complains about the "loading" tag in img.
+    # We need a more recent version for now.
+    commands:
+      - DEBIAN_FRONTEND=noninteractive apt update -qq
+      - DEBIAN_FRONTEND=noninteractive apt install -qq -y wget
+      - wget -q https://github.com/htacg/tidy-html5/releases/download/5.8.0/tidy-5.8.0-Linux-64bit.deb
+      - echo "59e594312207234f5a17455683c13c6bc47a89cb7bf994d493acfffb591d9830 tidy-5.8.0-Linux-64bit.deb" | sha256sum -c
+      - DEBIAN_FRONTEND=noninteractive apt install -qq -y ./tidy-5.8.0-Linux-64bit.deb
+      - tidy -q -e static/index.html
+
   - name: upload (preprod)
     when:
       branch: