diff --git a/.github/workflows/full_test.yml b/.github/workflows/full_test.yml
index e28bf37..84ddb20 100644
--- a/.github/workflows/full_test.yml
+++ b/.github/workflows/full_test.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python-version: ["3.9", "3.12"]
+        python-version: ["3.11"]
 
     steps:
       - uses: actions/checkout@v3
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..f103098
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,145 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a template Python library repository designed to be forked/used as a starting point for new Python packages. The library uses modern Python packaging standards with `hatchling` as the build backend.
+
+**Important naming distinction:**
+- **Package name** (used in imports): `my_library` (defined in `pyproject.toml` under `tool.hatch.build.targets.wheel.packages`)
+- **PyPI project name** (used for pip install): Can be different from package name (defined in `project.name`)
+
+## Development Commands
+
+### Testing and Quality Checks
+
+```bash
+# Run linting (uses ruff)
+make lint
+
+# Format code (uses ruff)
+make format
+
+# Run type checking (uses mypy)
+make typecheck
+
+# Run all tests
+make test
+
+# Run docstring tests (examples in docstrings)
+make doctest
+
+# Run all checks (lint, typecheck, test, doctest)
+make check
+
+# Generate coverage report (creates htmlcov/ directory)
+make coverage
+```
+
+### Building and Documentation
+
+```bash
+# Build the package (runs typecheck and test first)
+make build
+
+# Build documentation (uses mkdocs)
+make docs
+
+# Clean build artifacts
+make clean
+```
+
+### Running Individual Tests
+
+```bash
+# Run a single test file
+pytest tests/test_basic.py
+
+# Run a specific test function
+pytest tests/test_basic.py::test_module_docstring
+
+# Run with coverage for specific module
+pytest --cov=my_library tests/
+```
+
+## Code Quality Standards
+
+### Before Committing
+
+1. **Run ruff check** to catch linting errors that would fail CI:
+   ```bash
+   ruff check .
+   ```
+
+2. **Run ruff format** if the project uses ruff for formatting:
+   ```bash
+   ruff format .
+   ```
+
+### Ruff Configuration
+
+- Configured in `pyproject.toml` under `[tool.ruff]`
+- Long lines (E501) are ignored
+
+### Type Checking
+
+- Uses mypy with Python 3.11 target
+- Configuration in `pyproject.toml` under `[tool.mypy]`
+- `ignore_missing_imports = true` is set
+- Run via `make typecheck` or `mypy my_library/`
+
+## Package Structure
+
+```
+my_library/          # Main package code
+├── __init__.py     # Package initialization and docstring
+└── simulation.py   # Example module with Simulator class
+
+tests/              # Test suite
+├── __init__.py
+├── test_basic.py   # Basic tests
+└── data/           # Test data files
+
+docs/               # MkDocs documentation
+notebooks/          # Jupyter notebooks
+```
+
+## Documentation
+
+- Uses **MkDocs** with **Material theme**
+- Configured via `mkdocs.yml`
+- Uses **mkdocstrings** plugin for API documentation from docstrings
+- **Docstring style: NumPy** (not Google)
+- Docstrings should include executable examples that are tested with `make doctest`
+
+## CI/CD
+
+### GitHub Actions Workflows
+
+1. **full_test.yml**: Runs on push/PR to main
+   - Tests on Ubuntu and Windows
+   - Tests Python 3.11
+   - Runs: ruff linting, typecheck, pytest, doctest
+   - Uses `make` commands for consistency
+
+2. **docs.yml**: Builds and publishes documentation
+
+3. **python_publish.yml** and **python_publish_test.yml**: Package publishing workflows
+
+## Python Version Support
+
+- **Minimum Python version**: 3.11 (defined in `requires-python`)
+- CI tests on Python 3.11 only
+
+## Dependencies
+
+- **Runtime**: numpy
+- **Development**: build, pytest, ruff, mypy, mkdocs, mkdocstrings, mkdocs-material
+- **Testing**: pytest, pytest-cov, mypy
+- **Notebooks**: jupyter
+
+Install development dependencies:
+```bash
+pip install -e .[dev]
+```
diff --git a/pyproject.toml b/pyproject.toml
index 73ea87f..413cbb6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,7 +24,7 @@ authors = [
 ]
 description = "Useful library"
 readme = "README.md"
-requires-python = ">=3.9"
+requires-python = ">=3.11"
 license = {file = "LICENSE"}
 classifiers = [
     "Programming Language :: Python :: 3",
@@ -66,7 +66,7 @@ notebooks = [
 lint.ignore = ["E501"]
 
 [tool.mypy]
-python_version = "3.9"
+python_version = "3.11"
 ignore_missing_imports = true
 warn_unreachable = false
 no_implicit_optional = true