diff --git a/CLAUDE.md b/CLAUDE.md
index da266c6..fd8c929 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -8,6 +8,7 @@
 - use uv for dependency management and python version management
 - prefer using Python to other languages when it is appropriate
 - use Flask or Quart as a framework
+- use pytest for testing. Encourage and support a test-driven development (TDD) approach.
 
 ## JavaScript
 - use prettier for code formatting