diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 00000000..ca13f631
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,25 @@
+# General
+
+Follow .github/instructions/cpp.instructions.md
+
+# Naming
+
+Follow .github/instructions/cpp.instructions.md
+
+Exceptions:
+- Match existing external or legacy APIs (for example, public C API names and types that already use a different style).
+- Do not rename unrelated legacy identifiers in the same change unless the task requires it.
+
+# Test-driven development
+
+For every code change, follow strict TDD:
+
+1. Write or update automated tests that initially fail and describe the desired behavior and edge cases.
+2. Write the minimal production code needed to make the new tests pass. Do not add untested functionality.
+3. After tests are green, refactor tests and implementation for clarity and to remove duplication.
+4. Run the relevant tests after each refactor and keep them green.
+5. Repeat this red-green-refactor cycle in small steps.
+
+Structure tests with Arrange-Act-Assert and use descriptive names that capture intent, including negative and boundary cases.
+
+Never write production code first and wrap tests around it afterward. Tests must be written first and must fail before implementation.