diff --git a/.prettierignore b/.prettierignore
index 8a9086315e..fb9b694b75 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -10,3 +10,6 @@ stats
 .nyc_output
 # Autogenerated by `pnpm run --filter mermaid types:build-config`
 packages/mermaid/src/config.type.ts
+# Ignore the files creates in /demos/dev except for example.html
+demos/dev/**
+!/demos/dev/example.html
\ No newline at end of file