diff --git a/AGENTS.md b/AGENTS.md
index 2add69f..b4c7cda 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -100,6 +100,11 @@ uv run pytest tests/test_parser.py::TestParseTable::test_empty_input
 5. Joplin integration tests in `test_joplin.py` must mock `ClientApi` — do not
    require a live Joplin instance.
 
+6. **Keep `README.md` up to date.** When adding or changing functionality,
+   update the README to reflect it. Other agents read the README first for
+   project context — an outdated README leads to incorrect assumptions and
+   duplicate or conflicting work.
+
 # Behavioral Guidelines
 
 Behavioral guidelines to reduce common LLM coding mistakes. Merge with project-specific instructions as needed.