diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..7d5daf3
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,29 @@
+# deploydiff
+
+## Purpose
+Compare deployment configurations across environments. Detect drift between staging and production configs. Preview infrastructure changes with human-readable diffs, cost impact estimation, and rollback commands.
+
+## Build & Test Commands
+- Install: `pip install -e .` or `pip install deploydiff`
+- Test: `pytest tests/` (or `python -m pytest tests/ -v --tb=short`)
+- Lint: `ruff check .`
+- Build: `pip install build twine && python -m build && twine check dist/*`
+- CLI check: `deploydiff --help`
+
+## Architecture
+Key directories:
+- `src/deploydiff/` — Main package (CLI, diff engine, cost estimator, rollback generator)
+- `tests/` — Test suite
+- `.github/workflows/` — CI/CD (auto-code-review.yml, ci.yml, pages.yml, publish.yml)
+- `dist/` — Built distributions
+
+## Conventions
+- Language: Python 3.10+
+- Test framework: pytest
+- CI: GitHub Actions (auto-code-review.yml, ci.yml, pages.yml, publish.yml)
+- Linting: ruff
+- Build system: setuptools
+- Package layout: src/ layout
+- Dependencies: click, rich, pyyaml, tomli, jinja2
+- CLI entry point: deploydiff.cli:cli
+- Default branch: main
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
index 17077c0..d61a9a8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
 ]
 
 [project.optional-dependencies]