diff --git a/.gitignore b/.gitignore
index 69e72d3..8a9b06f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -173,3 +173,6 @@ cython_debug/
 
 # PyPI configuration file
 .pypirc
+
+# Doxygen output
+docs/doxygen/
diff --git a/Doxyfile b/Doxyfile
new file mode 100644
index 0000000..4948d7e
--- /dev/null
+++ b/Doxyfile
@@ -0,0 +1,16 @@
+# Doxygen configuration for the console calculator.
+# Generate the API documentation with:  doxygen Doxyfile
+PROJECT_NAME           = "Calculator"
+PROJECT_BRIEF          = "Console calculator (Udemy 100 Days of Code, day 10)"
+OUTPUT_DIRECTORY       = docs/doxygen
+INPUT                  = src
+FILE_PATTERNS          = *.py
+RECURSIVE              = YES
+OPTIMIZE_OUTPUT_JAVA   = YES
+EXTRACT_ALL            = YES
+EXTRACT_PRIVATE        = NO
+GENERATE_HTML          = YES
+GENERATE_LATEX         = NO
+QUIET                  = YES
+WARN_IF_UNDOCUMENTED   = YES
+WARN_NO_PARAMDOC       = YES
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..52745c6
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,22 @@
+[build-system]
+requires = ["setuptools>=69"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "calc"
+version = "0.1.0"
+description = "A console calculator (Udemy 100 Days of Code, day 10)."
+readme = "README.md"
+requires-python = ">=3.13"
+license = { text = "AGPL-3.0-or-later" }
+dependencies = []
+
+[project.optional-dependencies]
+dev = ["pytest>=8"]
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["src"]
diff --git a/src/calc/__init__.py b/src/calc/__init__.py
new file mode 100644
index 0000000..09888eb
--- /dev/null
+++ b/src/calc/__init__.py
@@ -0,0 +1,4 @@
+"""!
+@file __init__.py
+@brief Console calculator package (Udemy 100 Days of Code, day 10).
+"""
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29