diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index c7cd320..c692e94 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,21 +1,19 @@
 repos:
-  - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v4.1.0
-    hooks:
-      - id: trailing-whitespace
-        args: [--markdown-linebreak-ext=md]
-      - id: end-of-file-fixer
-      - id: check-yaml
-  - repo: https://github.com/psf/black
-    rev: 22.1.0
-    hooks:
-      - id: black
-  - repo: https://github.com/pycqa/isort
-    rev: 5.10.1
-    hooks:
-      - id: isort
-  - repo: https://github.com/PyCQA/flake8
-    rev: 4.0.1
-    hooks:
-      - id: flake8
-        args: [--max-line-length=88]
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v4.1.0
+  hooks:
+    - id: trailing-whitespace
+      args: [--markdown-linebreak-ext=md]
+    - id: end-of-file-fixer
+    - id: check-yaml
+  # ----- Python formatting -----
+- repo: https://github.com/charliermarsh/ruff-pre-commit
+  rev: v0.1.13
+  hooks:
+      # Run ruff linter.
+  - id: ruff
+    args:
+    - --quiet
+    - --fix
+      # Run ruff formatter.
+  - id: ruff-format
diff --git a/pydeps2env/__init__.py b/pydeps2env/__init__.py
new file mode 100644
index 0000000..74db84b
--- /dev/null
+++ b/pydeps2env/__init__.py
@@ -0,0 +1,5 @@
+"""pydeps2env: helps to generate conda environment files from python package dependencies."""
+
+from .environment import Environment
+
+__all__ = ["Environment"]
diff --git a/pydeps2env/environment.py b/pydeps2env/environment.py
new file mode 100644
index 0000000..f752aad
--- /dev/null
+++ b/pydeps2env/environment.py
@@ -0,0 +1,111 @@
+from dataclasses import dataclass, field
+from packaging.requirements import Requirement
+from pathlib import Path
+from collections import defaultdict
+import tomli as tomllib
+import yaml
+import warnings
+
+
+def add_requirement(
+    req: Requirement | str,
+    requirements: dict[str, Requirement],
+    mode: str = "combine",
+):
+    """Add a requirement to existing requirement specification (in place)."""
+
+    if not isinstance(req, Requirement):
+        req = Requirement(req)
+
+    if req.name not in requirements:
+        requirements[req.name] = req
+    elif mode == "combine":
+        requirements[req.name].specifier &= req.specifier
+    elif mode == "replace":
+        requirements[req.name] = req
+    else:
+        raise ValueError(f"Unknown `mode` for add_requirement: {mode}")
+
+
+def combine_requirements(
+    req1: dict[str, Requirement], req2: dict[str, Requirement]
+) -> dict[str, Requirement]:
+    """Combine multiple requirement listings."""
+    req1 = req1.copy()
+    for r in req2.values():
+        add_requirement(r, req1, mode="combine")
+
+    return req1
+
+
+@dataclass
+class Environment:
+    filename: str | Path
+    channels: list[str] = field(default_factory=lambda: ["conda-forge"])
+    pip_packages: set[str] = field(default_factory=set)  # install via pip
+    requirements: dict[str, Requirement] = field(default_factory=dict, init=False)
+    build_system: dict[str, Requirement] = field(default_factory=dict, init=False)
+
+    def __post_init__(self):
+        if Path(self.filename).suffix == ".toml":
+            self.load_pyproject()
+
+    def load_pyproject(self):
+        with open(self.filename, "rb") as fh:
+            cp = defaultdict(dict, tomllib.load(fh))
+
+        if python := cp["project"].get("requires-python"):
+            add_requirement("python" + python, self.requirements)
+
+        for dep in cp.get("project").get("dependencies"):
+            add_requirement(dep, self.requirements)
+
+        for dep in cp.get("build-system").get("requires"):
+            add_requirement(dep, self.build_system)
+
+    def _get_dependencies(self, include_build_system: bool = True):
+        """Get the default conda environment entries."""
+
+        reqs = self.requirements.copy()
+        if include_build_system:
+            reqs = combine_requirements(reqs, self.build_system)
+
+        _python = reqs.pop("python", None)
+
+        deps = [str(r) for r in reqs.values() if r.name not in self.pip_packages]
+        deps.sort(key=str.lower)
+        if _python:
+            deps = [str(_python)] + deps
+
+        pip = [str(r) for r in reqs.values() if r.name in self.pip_packages]
+        pip.sort(key=str.lower)
+
+        return deps, pip
+
+    def export(
+        self,
+        outfile: str | Path = "environment.yaml",
+        include_build_system: bool = True,
+    ):
+        deps, pip = self._get_dependencies(include_build_system=include_build_system)
+
+        conda_env = {"channels": self.channels, "dependencies": deps.copy()}
+        if pip:
+            conda_env["dependencies"] += ["pip", {"pip": pip}]
+
+        if outfile is None:
+            return conda_env
+
+        p = Path(outfile)
+        if p.suffix in [".txt"]:
+            deps += pip
+            deps.sort(key=str.lower)
+            with open(p, "w") as outfile:
+                outfile.writelines("\n".join(deps))
+        else:
+            if p.suffix not in [".yaml", ".yml"]:
+                warnings.warn(
+                    f"Unknown environment format `{p.suffix}`, generating conda yaml output."
+                )
+            with open(p, "w") as outfile:
+                yaml.dump(conda_env, outfile, default_flow_style=False)