diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..c08a655
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,8 @@
+# Regeln für dieses Projekt
+- Code nach PEP 8, Zeilenlänge maximal 88 Zeichen.
+- Jede Funktion und Methode hat einen Docstring und Type Hints.
+- Vor jedem Commit: `ruff check` und `ruff format`.
+
+## Projektstruktur
+- Quellcode liegt unter "src/matrixmania/", Tests unter "test/test_matrixmania/"
+- Testpakete, Testdateien und Testfunktionen beginnen mit "test_"
\ No newline at end of file
diff --git a/install_dependencies.py b/install_dependencies.py
new file mode 100644
index 0000000..5a20e39
--- /dev/null
+++ b/install_dependencies.py
@@ -0,0 +1,146 @@
+#!/usr/bin/env python3
+"""Installiert die Abhängigkeiten aus pyproject.toml in die aktuelle Python-Umgebung.
+
+Ersatz für "Install requirements" aus PyCharm, wenn das Projekt eine pyproject.toml
+statt einer requirements.txt hat. Kein Build, keine besondere Projektstruktur nötig,
+nur Standardbibliothek (Python >= 3.11).
+
+Benutzung:
+  In PyCharm: Rechtsklick auf diese Datei -> Run 'install_dependencies'
+  Im Terminal (venv aktiv): python install_dependencies.py
+
+Ohne Parameter wird ALLES installiert:
+  [project].dependencies + alle [project.optional-dependencies] + alle [dependency-groups]
+
+Abweichendes Verhalten:
+  python install_dependencies.py --extra dev        nur Basis + Extra "dev"
+  python install_dependencies.py --group test       nur Basis + Gruppe "test"
+  python install_dependencies.py --no-main --group dev
+  python install_dependencies.py --list             nur anzeigen, nichts installieren
+  python install_dependencies.py --write            requirements.txt schreiben statt installieren
+  python install_dependencies.py --write -o reqs.txt
+"""
+from __future__ import annotations
+
+import sys
+
+if sys.version_info < (3, 11):
+    sys.exit("Dieses Skript braucht Python 3.11 oder neuer (tomllib). "
+             f"Aktuell: {sys.version.split()[0]}")
+
+import argparse
+import subprocess
+import tempfile
+import tomllib
+from pathlib import Path
+
+PROJECT_DIR = Path(__file__).resolve().parent
+
+
+def resolve_group(groups: dict, name: str, seen: set[str] | None = None) -> list[str]:
+    """Löst eine Dependency-Group inkl. {include-group = "..."} rekursiv auf."""
+    seen = set() if seen is None else seen
+    if name in seen:
+        raise ValueError(f"Zyklische include-group: {name}")
+    if name not in groups:
+        raise KeyError(f"Dependency-Group '{name}' nicht gefunden")
+    seen.add(name)
+    result: list[str] = []
+    for entry in groups[name]:
+        if isinstance(entry, str):
+            result.append(entry)
+        elif isinstance(entry, dict) and "include-group" in entry:
+            result.extend(resolve_group(groups, entry["include-group"], seen))
+    return result
+
+
+def collect(data: dict, extras: list[str], groups: list[str], no_main: bool) -> list[str]:
+    project = data.get("project", {})
+    optional = project.get("optional-dependencies", {})
+    dep_groups = data.get("dependency-groups", {})
+    deps: list[str] = []
+
+    if not no_main:
+        deps.extend(project.get("dependencies", []))
+    for extra in extras:
+        if extra not in optional:
+            raise KeyError(f"Optional-Dependency '{extra}' nicht gefunden")
+        deps.extend(optional[extra])
+    for group in groups:
+        deps.extend(resolve_group(dep_groups, group))
+
+    # Duplikate entfernen, Reihenfolge behalten
+    return list(dict.fromkeys(d.strip() for d in deps if d.strip()))
+
+
+def main() -> int:
+    p = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    p.add_argument("-p", "--pyproject", type=Path, default=PROJECT_DIR / "pyproject.toml",
+                   help="Pfad zur pyproject.toml (Standard: neben diesem Skript)")
+    p.add_argument("--extra", action="append", default=None,
+                   help="nur diese optional-dependencies (mehrfach möglich)")
+    p.add_argument("--group", action="append", default=None,
+                   help="nur diese dependency-groups (mehrfach möglich)")
+    p.add_argument("--no-main", action="store_true", help="[project].dependencies weglassen")
+    p.add_argument("--list", action="store_true", help="Abhängigkeiten nur anzeigen")
+    p.add_argument("--write", action="store_true", help="requirements-Datei schreiben statt installieren")
+    p.add_argument("-o", "--output", type=Path, default=PROJECT_DIR / "requirements.txt",
+                   help="Zieldatei für --write")
+    args = p.parse_args()
+
+    if not args.pyproject.exists():
+        print(f"{args.pyproject} nicht gefunden", file=sys.stderr)
+        return 1
+    data = tomllib.loads(args.pyproject.read_text(encoding="utf-8"))
+    all_extras = list(data.get("project", {}).get("optional-dependencies", {}))
+    all_groups = list(data.get("dependency-groups", {}))
+
+    # Ohne --extra/--group: alles. Mit einem davon: nur das Gewählte.
+    selective = args.extra is not None or args.group is not None
+    extras = (args.extra or []) if selective else all_extras
+    groups = (args.group or []) if selective else all_groups
+
+    try:
+        deps = collect(data, extras, groups, args.no_main)
+    except (KeyError, ValueError) as e:
+        print(f"Fehler: {e.args[0]}", file=sys.stderr)
+        print(f"  Vorhandene --extra: {', '.join(all_extras) or '(keine)'}", file=sys.stderr)
+        print(f"  Vorhandene --group: {', '.join(all_groups) or '(keine)'}", file=sys.stderr)
+        return 1
+
+    parts = ([] if args.no_main else ["Basis"]) + [f"extra:{e}" for e in extras] + [f"group:{g}" for g in groups]
+    print(f"Auswahl: {', '.join(parts) or '(nichts)'}")
+
+    if args.list:
+        print("\n".join(deps) or "(keine Abhängigkeiten)")
+        return 0
+
+    content = f"# Automatisch erzeugt aus {args.pyproject.name} – nicht von Hand bearbeiten\n" + "\n".join(deps) + "\n"
+
+    if args.write:
+        args.output.write_text(content, encoding="utf-8")
+        print(f"{len(deps)} Abhängigkeiten -> {args.output}")
+        return 0
+
+    if not deps:
+        print("Keine Abhängigkeiten gefunden – nichts zu tun.")
+        return 0
+
+    if sys.prefix == sys.base_prefix:
+        print("WARNUNG: Es ist kein virtuelles Environment aktiv – es wird in die globale "
+              f"Python-Installation installiert:\n  {sys.prefix}", file=sys.stderr)
+        if sys.stdin.isatty() and input("Trotzdem fortfahren? [j/N] ").strip().lower() not in ("j", "ja", "y", "yes"):
+            return 1
+
+    with tempfile.NamedTemporaryFile("w", suffix=".txt", delete=False, encoding="utf-8") as tmp:
+        tmp.write(content)
+        tmp_path = Path(tmp.name)
+    try:
+        print(f"Installiere {len(deps)} Abhängigkeiten in {sys.prefix}\n")
+        return subprocess.call([sys.executable, "-m", "pip", "install", "-r", str(tmp_path)])
+    finally:
+        tmp_path.unlink(missing_ok=True)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..f2ac542
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,10 @@
+[project]
+name = "matrixmania"
+version = "0.1.0"
+dependencies = ["tabulate", "ruff"]
+
+[project.optional-dependencies]
+dev = ["pytest", "ruff", "pytest-cov"]
+
+[tool.pytest.ini_options]
+pythonpath = "src"
\ No newline at end of file
diff --git a/test/test_matrixmania/__init__.py b/test/test_matrixmania/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/test/test_matrixmania/test_projection.py b/test/test_matrixmania/test_projection.py
new file mode 100644
index 0000000..43f9d7e
--- /dev/null
+++ b/test/test_matrixmania/test_projection.py
@@ -0,0 +1,24 @@
+from matrixmania import project_ortho
+
+def test_project_ortho_without_scale() -> None:
+    """Orthogonal projection ignores z when scale is omitted."""
+    # Arrange
+    point = (1.0, 2.0, 3.0)
+
+    # Act
+    result = project_ortho(point)
+
+    # Assert
+    assert result == (1.0, 2.0)
+
+def test_project_ortho_with_scale() -> None:
+    """Orthogonal projection scales x and y and ignores z."""
+    # Arrange
+    point = (1.0, 2.0, 3.0)
+    scale = 100
+
+    # Act
+    result = (project_ortho(point, scale=scale))
+
+    # Assert
+    assert result == (100.0, 200.0)
diff --git a/test/test_matrixmania/test_rot.py b/test/test_matrixmania/test_rot.py
new file mode 100644
index 0000000..dafe8ec
--- /dev/null
+++ b/test/test_matrixmania/test_rot.py
@@ -0,0 +1,102 @@
+import math
+
+import pytest
+
+from matrixmania import rot_2D, rot_3D
+
+
+def test_rot_2d_quarter_turn() -> None:
+    """A quarter turn rotates a 2D point counterclockwise."""
+    # Arrange
+    angle = math.pi / 2
+
+    # Act
+    result = rot_2D(angle)
+
+    # Assert
+    assert result[0] == pytest.approx([0.0, -1.0])
+    assert result[1] == pytest.approx([1.0, 0.0])
+
+
+def test_rot_3d_around_x_axis() -> None:
+    """A quarter turn returns the expected matrix around x."""
+    # Arrange
+    angle = math.pi / 2
+    expected = [[1.0, 0.0, 0.0], [0.0, 0.0, -1.0], [0.0, 1.0, 0.0]]
+
+    # Act
+    result = rot_3D(angle, "x")
+
+    # Assert
+    for actual_row, expected_row in zip(result, expected):
+        assert actual_row == pytest.approx(expected_row)
+
+
+def test_rot_3d_around_y_axis() -> None:
+    """A quarter turn returns the expected matrix around y."""
+    # Arrange
+    angle = math.pi / 2
+    expected = [[0.0, 0.0, 1.0], [0.0, 1.0, 0.0], [-1.0, 0.0, 0.0]]
+
+    # Act
+    result = rot_3D(angle, "y")
+
+    # Assert
+    for actual_row, expected_row in zip(result, expected):
+        assert actual_row == pytest.approx(expected_row)
+
+
+def test_rot_3d_around_z_axis() -> None:
+    """A quarter turn returns the expected matrix around z."""
+    # Arrange
+    angle = math.pi / 2
+    expected = [[0.0, -1.0, 0.0], [1.0, 0.0, 0.0], [0.0, 0.0, 1.0]]
+
+    # Act
+    result = rot_3D(angle, "z")
+
+    # Assert
+    for actual_row, expected_row in zip(result, expected):
+        assert actual_row == pytest.approx(expected_row)
+
+
+def test_rot_3d_rejects_empty_axis() -> None:
+    """An empty axis is invalid."""
+    # Arrange
+    angle = math.pi / 2
+    axis = ""
+
+    # Act
+    with pytest.raises(ValueError) as error:
+        rot_3D(angle, axis)
+
+    # Assert
+    assert str(error.value) == "axis must be 'x', 'y', or 'z'"
+
+
+def test_rot_3d_rejects_unknown_axis() -> None:
+    """An unknown axis is invalid."""
+    # Arrange
+    angle = math.pi / 2
+    axis = "a"
+
+    # Act
+    with pytest.raises(ValueError) as error:
+        rot_3D(angle, axis)
+
+    # Assert
+    assert str(error.value) == "axis must be 'x', 'y', or 'z'"
+
+
+def test_rot_3d_rejects_uppercase_axis() -> None:
+    """Axis values must be lowercase."""
+    # Arrange
+    angle = math.pi / 2
+    axis = "X"
+
+    # Act
+    with pytest.raises(ValueError) as error:
+        rot_3D(angle, axis)
+
+    # Assert
+    assert str(error.value) == "axis must be 'x', 'y', or 'z'"