diff --git a/.planning/PROJECT.md b/.planning/PROJECT.md
index c76cbac..002b728 100644
--- a/.planning/PROJECT.md
+++ b/.planning/PROJECT.md
@@ -78,6 +78,7 @@ The product uses debate/speech terminology throughout:
 - **Build environment**: ISO builds run in sandboxed environment for security
 - **Performance**: 3D UI must run at 60fps on mid-range hardware; 2D fallback for low-end devices
 - **Independence**: No upstream coordination with Omarchy - must be resilient to their changes
+- **Python tooling**: Use ruff for linting and formatting (replaces flake8, black, isort)
 
 ## Key Decisions
 
@@ -88,6 +89,7 @@ The product uses debate/speech terminology throughout:
 | Debate terminology | Creates memorable brand identity; "debate opinions" is the product concept | - Pending |
 | Self-hosted infrastructure | Build server already available; full control over build environment | - Pending |
 | Greenfield implementation | No legacy constraints; can build architecture correctly from start | - Pending |
+| Ruff for Python tooling | Fast, replaces flake8+black+isort; better DX with single tool | - Pending |
 
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 *Last updated: 2026-01-25 after initialization*