diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 2fa22d6..9f9ff15 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -24,8 +24,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version:
-        - "2.7"
-        - "3.5"
+        - "3.6"
         - "3.8"
         - "3.9"
         - "3.10"
@@ -46,5 +45,4 @@ jobs:
       run: python -m pytest --doctest-modules --cov=src/hepunits --cov-report=xml
 
     - name: Test coverage with Codecov
-      if: matrix.python-version != '3.5' && matrix.python-version != '3.8'
       uses: codecov/codecov-action@v2
diff --git a/.gitignore b/.gitignore
index 9b72556..f102fcc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -71,3 +71,4 @@ docs/_build
 /.mypy_cache/*
 /pip-wheel-metadata/*
 /src/hepunits/version.py
+/src/hepunits/_version.py
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d7c8343..67d1102 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,16 +1,10 @@
 
 repos:
-- repo: https://github.com/psf/black
-  rev: 21.12b0
-  hooks:
-  - id: black
-
 - repo: https://github.com/pre-commit/pre-commit-hooks
   rev: v4.1.0
   hooks:
   - id: debug-statements
   - id: end-of-file-fixer
-  - id: fix-encoding-pragma
   - id: mixed-line-ending
   - id: requirements-txt-fixer
   - id: trailing-whitespace
@@ -20,6 +14,17 @@ repos:
   - id: check-symlinks
   - id: check-yaml
 
+- repo: https://github.com/asottile/pyupgrade
+  rev: v2.31.0
+  hooks:
+  - id: pyupgrade
+    args: [--py36-plus]
+
+- repo: https://github.com/psf/black
+  rev: 21.12b0
+  hooks:
+  - id: black-jupyter
+
 - repo: https://github.com/mgedmin/check-manifest
   rev: "0.47"
   hooks:
@@ -36,10 +41,32 @@ repos:
   rev: v0.931
   hooks:
   - id: mypy
-    args: [--strict]
     files: src
+    args: [--show-error-codes]
 
-- repo: https://github.com/asottile/pyupgrade
-  rev: v2.31.0
+- repo: https://github.com/asottile/setup-cfg-fmt
+  rev: v1.20.0
   hooks:
-  - id: pyupgrade
+  - id: setup-cfg-fmt
+
+- repo: https://github.com/PyCQA/isort
+  rev: 5.10.1
+  hooks:
+  - id: isort
+
+- repo: https://github.com/codespell-project/codespell
+  rev: v2.1.0
+  hooks:
+  - id: codespell
+
+- repo: https://github.com/pre-commit/pygrep-hooks
+  rev: v1.9.0
+  hooks:
+  - id: python-check-blanket-noqa
+  - id: python-check-blanket-type-ignore
+  - id: python-no-log-warn
+  - id: python-no-eval
+  - id: python-use-type-annotations
+  - id: rst-backticks
+  - id: rst-directive-colons
+  - id: rst-inline-touching-normal
diff --git a/MANIFEST.in b/MANIFEST.in
index 57bb7b9..939fe5e 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -5,6 +5,6 @@ include pyproject.toml
 recursive-include tests *.py
 
 # Type support
-recursive-include src py.typed
+recursive-include src py.typed *.pyi
 
 exclude .pre-commit-config.yaml codecov.yml
diff --git a/README.rst b/README.rst
index 9e65bb2..bba62ef 100644
--- a/README.rst
+++ b/README.rst
@@ -136,10 +136,10 @@ These simple rules are enough - exemplified in the code below:
 - Dimensioned quantities in the "data stores" abide to the HEP system of units.
 
 - All definitions of dimensioned quantities are dimensioned by multiplying by the units,
-  as in `mass_window = 500 * keV`.
+  as in ``mass_window = 500 * keV``.
 
 - All output of dimensioned quantities is converted to the required units
-  by dividing by the units, as in `energy_resolution() / GeV`.
+  by dividing by the units, as in ``energy_resolution() / GeV``.
 
 For the sake of argument, let's consider below a function returning a dimensioned quantity.
 the function below stores a dimensioned quantity defined in keV
diff --git a/noxfile.py b/noxfile.py
new file mode 100644
index 0000000..0219f0d
--- /dev/null
+++ b/noxfile.py
@@ -0,0 +1,19 @@
+import nox
+
+
+@nox.session
+def lint(session: nox.Session) -> None:
+    """
+    Run the linter.
+    """
+    session.install("pre-commit")
+    session.run("pre-commit", "run", "--all-files", *session.posargs)
+
+
+@nox.session(python=["3.6", "3.7", "3.8", "3.9", "3.10"])
+def tests(session: nox.Session) -> None:
+    """
+    Run the unit and regular tests.
+    """
+    session.install(".[test]")
+    session.run("pytest", *session.posargs)
diff --git a/pyproject.toml b/pyproject.toml
index 3392c13..47e06f5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -6,10 +6,35 @@ requires = [
 ]
 build-backend = "setuptools.build_meta"
 
+
 [tool.setuptools_scm]
-write_to = "src/hepunits/version.py"
+write_to = "src/hepunits/_version.py"
+
+
+[tool.isort]
+profile = "black"
+
+
+[tool.pytest.ini_options]
+minversion = "6.0"
+junit_family = "xunit2"
+testpaths = ["tests"]
+filterwarnings = ["error"]
+addopts = ["-ra", "--showlocals", "--strict-markers", "--strict-config"]
+xfail_strict = true
+log_cli_level = "DEBUG"
+
 
 [tool.check-manifest]
 ignore = [
-    "src/hepunits/version.py",
+    "src/hepunits/_version.py",
+    ".pre-commit-config.yaml",
+    "noxfile.py",
 ]
+
+
+[tool.mypy]
+warn_unused_configs = true
+python_version = "3.6"
+files = ["src"]
+strict = true
diff --git a/setup.cfg b/setup.cfg
index 2e2c899..5c52b28 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,90 +1,63 @@
-[bdist_wheel]
-universal=1
-
-
 [metadata]
 name = hepunits
-author = Eduardo Rodrigues
-author_email = eduardo.rodrigues@cern.ch
-maintainer = Eduardo Rodrigues
-maintainer_email = eduardo.rodrigues@cern.ch
 description = Units and constants in the HEP system of units
 long_description = file: README.rst
 long_description_content_type = text/x-rst
 url = https://github.com/scikit-hep/hepunits
+author = Eduardo Rodrigues
+author_email = eduardo.rodrigues@cern.ch
+maintainer = Eduardo Rodrigues
+maintainer_email = eduardo.rodrigues@cern.ch
 license = BSD-3-Clause
-classifier =
-    Topic :: Scientific/Engineering
-    Intended Audience :: Science/Research
+license_file = LICENSE
+classifiers =
+    Development Status :: 5 - Production/Stable
     Intended Audience :: Developers
-    Operating System :: OS Independent
+    Intended Audience :: Science/Research
     License :: OSI Approved :: BSD License
+    Operating System :: OS Independent
     Programming Language :: Python
-    Programming Language :: Python :: 2
-    Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
-    Development Status :: 5 - Production/Stable
+    Topic :: Scientific/Engineering
 keywords =
     HEP
     HEP system of units
     Units
     Constants
 
-
 [options]
-python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*
+packages = find:
+python_requires = >=3.6
 include_package_data = True
-zip_safe = False
-packages: find:
 package_dir =
     =src
-
-
+zip_safe = False
 
 [options.packages.find]
 where = src
 
-
-[options.package_data]
-* = py.typed
-
-[tool:pytest]
-junit_family=xunit2
-testpaths =
-    tests
-addopts = -Wd
-
-
 [options.extras_require]
-test =
-  pytest >=4.6
-  pytest-cov >=2.8.0
-dev =
-  pytest >=4.6
-  pytest-cov >=2.8.0
 all =
-  pytest >=4.6
-  pytest-cov >=2.8.0
-
-[check-manifest]
-ignore =
-    src/hepunits/version.py
-    .pre-commit-config.yaml
-
-[mypy]
-strict=True
-
-[mypy-hepunits.version]
-ignore_missing_imports = True
+    pytest>=6
+    pytest-cov>=2.8.0
+dev =
+    pytest>=6
+    pytest-cov>=2.8.0
+test =
+    pytest>=6
+    pytest-cov>=2.8.0
 
+[options.package_data]
+* = py.typed
 
 [flake8]
-max-complexity = 12
-ignore = E203, E231, E501, E722, W503, F401, F403, F405
+extend-ignore = B950, E501
 select = C,E,F,W,B,B9,T
+per-file-ignores =
+    tests/*: T, F405, F403
diff --git a/setup.py b/setup.py
index ced15ef..d1c1fd0 100644
--- a/setup.py
+++ b/setup.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 
 from setuptools import setup
diff --git a/src/hepunits/__init__.py b/src/hepunits/__init__.py
index d42f95f..9a7b6c3 100644
--- a/src/hepunits/__init__.py
+++ b/src/hepunits/__init__.py
@@ -1,9 +1,496 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 
 # Convenient access to the version number
-from .version import version as __version__
+from typing import List
+
+from . import constants, units
+from ._version import version as __version__
+from .constants.constants import (
+    Avogadro,
+    c_light,
+    c_light_sq,
+    e_sq,
+    eminus,
+    h_Planck,
+    half_pi,
+    hbar,
+    hbar_Planck,
+    hbarc,
+    hbarc_sq,
+    k_Boltzmann,
+    pi,
+    pi_sq,
+    two_pi,
+)
+from .units.prefixes import (
+    atto,
+    centi,
+    deca,
+    deci,
+    exa,
+    exbi,
+    femto,
+    gibi,
+    giga,
+    googol,
+    hecto,
+    kibi,
+    kilo,
+    mebi,
+    mega,
+    micro,
+    milli,
+    nano,
+    pebi,
+    peta,
+    pico,
+    tebi,
+    tera,
+    yobi,
+    yocto,
+    yotta,
+    zebi,
+    zepto,
+    zetta,
+)
+from .units.units import (
+    GW,
+    MW,
+    A,
+    Bq,
+    Ci,
+    EeV,
+    GBq,
+    GeV,
+    GHz,
+    Gy,
+    Hz,
+    J,
+    MBq,
+    MeV,
+    MGy,
+    MHz,
+    N,
+    Pa,
+    PeV,
+    Sv,
+    TeV,
+    THz,
+    W,
+    ZeV,
+    ab,
+    ampere,
+    angstrom,
+    atmosphere,
+    attobarn,
+    attosecond,
+    bar,
+    barn,
+    becquerel,
+    candela,
+    cd,
+    centimeter,
+    centimeter2,
+    centimeter3,
+    cm,
+    cm2,
+    cm3,
+    coulomb,
+    curie,
+    d,
+    day,
+    deg,
+    degree,
+    dyne,
+    e_SI,
+    electronvolt,
+    eplus,
+    erg,
+    eV,
+    exaelectronvolt,
+    farad,
+    fb,
+    femtobarn,
+    femtometer,
+    femtosecond,
+    fermi,
+    fm,
+    fm2,
+    fm3,
+    fs,
+    g,
+    gauss,
+    gigabecquerel,
+    gigaelectronvolt,
+    gigahertz,
+    gram,
+    gray,
+    h,
+    henry,
+    hertz,
+    hour,
+    invab,
+    invfb,
+    invmb,
+    invnb,
+    invpb,
+    invub,
+    joule,
+    kBq,
+    kelvin,
+    keV,
+    kg,
+    kGy,
+    kHz,
+    kilobecquerel,
+    kiloelectronvolt,
+    kilogauss,
+    kilogram,
+    kilogray,
+    kilohertz,
+    kilometer,
+    kilometer2,
+    kilometer3,
+    kilovolt,
+    km,
+    km2,
+    km3,
+    kW,
+    lumen,
+    lux,
+    m,
+    m2,
+    m3,
+    mb,
+    mCi,
+    megabecquerel,
+    megaelectronvolt,
+    megagray,
+    megahertz,
+    megavolt,
+    meter,
+    meter2,
+    meter3,
+    mg,
+    mGy,
+    microampere,
+    microbarn,
+    microcurie,
+    microfarad,
+    microgray,
+    micrometer,
+    micron,
+    microsecond,
+    milliampere,
+    millibarn,
+    millicurie,
+    millifarad,
+    milligram,
+    milligray,
+    millimeter,
+    millimeter2,
+    millimeter3,
+    milliradian,
+    millisecond,
+    minute,
+    mm,
+    mm2,
+    mm3,
+    mol,
+    mole,
+    mrad,
+    ms,
+    nanoampere,
+    nanobarn,
+    nanocurie,
+    nanofarad,
+    nanometer,
+    nanosecond,
+    nb,
+    nCi,
+    newton,
+    ns,
+    ohm,
+    pascal,
+    pb,
+    petaelectronvolt,
+    picobarn,
+    picofarad,
+    picosecond,
+    ps,
+    rad,
+    radian,
+    s,
+    second,
+    sievert,
+    sr,
+    steradian,
+    teraelectronvolt,
+    terahertz,
+    tesla,
+    ub,
+    uCi,
+    uGy,
+    us,
+    volt,
+    watt,
+    weber,
+    y,
+    year,
+    yoctosecond,
+    ys,
+    zeptosecond,
+    zettaelectronvolt,
+    zs,
+)
 
 # Units and constants directly available
-from .units import *
-from .constants import *
+
+
+__all__ = (
+    "units",
+    "constants",
+    "atto",
+    "centi",
+    "deca",
+    "deci",
+    "exa",
+    "exbi",
+    "femto",
+    "gibi",
+    "giga",
+    "googol",
+    "hecto",
+    "kibi",
+    "kilo",
+    "mebi",
+    "mega",
+    "micro",
+    "milli",
+    "nano",
+    "pebi",
+    "peta",
+    "pico",
+    "tebi",
+    "tera",
+    "yobi",
+    "yocto",
+    "yotta",
+    "zebi",
+    "zepto",
+    "zetta",
+    "A",
+    "Bq",
+    "Ci",
+    "EeV",
+    "GBq",
+    "GHz",
+    "GW",
+    "GeV",
+    "Gy",
+    "Hz",
+    "J",
+    "MBq",
+    "MGy",
+    "MHz",
+    "MW",
+    "MeV",
+    "N",
+    "Pa",
+    "PeV",
+    "Sv",
+    "THz",
+    "TeV",
+    "W",
+    "ZeV",
+    "ab",
+    "ampere",
+    "angstrom",
+    "atmosphere",
+    "attobarn",
+    "attosecond",
+    "bar",
+    "barn",
+    "becquerel",
+    "candela",
+    "cd",
+    "centimeter",
+    "centimeter2",
+    "centimeter3",
+    "cm",
+    "cm2",
+    "cm3",
+    "coulomb",
+    "curie",
+    "d",
+    "day",
+    "deg",
+    "degree",
+    "dyne",
+    "eV",
+    "e_SI",
+    "electronvolt",
+    "eplus",
+    "erg",
+    "exaelectronvolt",
+    "farad",
+    "fb",
+    "femtobarn",
+    "femtometer",
+    "femtosecond",
+    "fermi",
+    "fm",
+    "fm2",
+    "fm3",
+    "fs",
+    "g",
+    "gauss",
+    "gigabecquerel",
+    "gigaelectronvolt",
+    "gigahertz",
+    "gram",
+    "gray",
+    "h",
+    "henry",
+    "hertz",
+    "hour",
+    "invab",
+    "invfb",
+    "invmb",
+    "invnb",
+    "invpb",
+    "invub",
+    "joule",
+    "kBq",
+    "kGy",
+    "kHz",
+    "kW",
+    "keV",
+    "kelvin",
+    "kg",
+    "kilobecquerel",
+    "kiloelectronvolt",
+    "kilogauss",
+    "kilogram",
+    "kilogray",
+    "kilohertz",
+    "kilometer",
+    "kilometer2",
+    "kilometer3",
+    "kilovolt",
+    "km",
+    "km2",
+    "km3",
+    "lumen",
+    "lux",
+    "m",
+    "m2",
+    "m3",
+    "mCi",
+    "mGy",
+    "mb",
+    "megabecquerel",
+    "megaelectronvolt",
+    "megagray",
+    "megahertz",
+    "megavolt",
+    "meter",
+    "meter2",
+    "meter3",
+    "mg",
+    "microampere",
+    "microbarn",
+    "microcurie",
+    "microfarad",
+    "microgray",
+    "micrometer",
+    "micron",
+    "microsecond",
+    "milliampere",
+    "millibarn",
+    "millicurie",
+    "millifarad",
+    "milligram",
+    "milligray",
+    "millimeter",
+    "millimeter2",
+    "millimeter3",
+    "milliradian",
+    "millisecond",
+    "minute",
+    "mm",
+    "mm2",
+    "mm3",
+    "mol",
+    "mole",
+    "mrad",
+    "ms",
+    "nCi",
+    "nanoampere",
+    "nanobarn",
+    "nanocurie",
+    "nanofarad",
+    "nanometer",
+    "nanosecond",
+    "nb",
+    "newton",
+    "ns",
+    "ohm",
+    "pascal",
+    "pb",
+    "petaelectronvolt",
+    "picobarn",
+    "picofarad",
+    "picosecond",
+    "ps",
+    "rad",
+    "radian",
+    "s",
+    "second",
+    "sievert",
+    "sr",
+    "steradian",
+    "teraelectronvolt",
+    "terahertz",
+    "tesla",
+    "uCi",
+    "uGy",
+    "ub",
+    "us",
+    "volt",
+    "watt",
+    "weber",
+    "y",
+    "year",
+    "yoctosecond",
+    "ys",
+    "zeptosecond",
+    "zettaelectronvolt",
+    "zs",
+    "m",
+    "s",
+    "eplus",
+    "mole",
+    "joule",
+    "kelvin",
+    "c_light",
+    "c_light_sq",
+    "pi",
+    "two_pi",
+    "half_pi",
+    "pi_sq",
+    "eminus",
+    "e_sq",
+    "Avogadro",
+    "h_Planck",
+    "hbar_Planck",
+    "hbar",
+    "hbarc",
+    "hbarc_sq",
+    "k_Boltzmann",
+    "__version__",
+)
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/src/hepunits/_version.pyi b/src/hepunits/_version.pyi
new file mode 100644
index 0000000..5bb2b22
--- /dev/null
+++ b/src/hepunits/_version.pyi
@@ -0,0 +1,2 @@
+version: str
+version_tuple: tuple[int, int, int] | tuple[int, int, int, str, str]
diff --git a/src/hepunits/constants/__init__.py b/src/hepunits/constants/__init__.py
index 2a5d84c..1c3957a 100644
--- a/src/hepunits/constants/__init__.py
+++ b/src/hepunits/constants/__init__.py
@@ -1,4 +1,57 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 
-from .constants import *
+from typing import List
+
+from . import constants
+from .constants import (
+    Avogadro,
+    c_light,
+    c_light_sq,
+    e_sq,
+    eminus,
+    eplus,
+    h_Planck,
+    half_pi,
+    hbar,
+    hbar_Planck,
+    hbarc,
+    hbarc_sq,
+    joule,
+    k_Boltzmann,
+    kelvin,
+    m,
+    mole,
+    pi,
+    pi_sq,
+    s,
+    two_pi,
+)
+
+__all__ = (
+    "constants",
+    "m",
+    "s",
+    "eplus",
+    "mole",
+    "joule",
+    "kelvin",
+    "c_light",
+    "c_light_sq",
+    "pi",
+    "two_pi",
+    "half_pi",
+    "pi_sq",
+    "eminus",
+    "e_sq",
+    "Avogadro",
+    "h_Planck",
+    "hbar_Planck",
+    "hbar",
+    "hbarc",
+    "hbarc_sq",
+    "k_Boltzmann",
+)
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/src/hepunits/constants/constants.py b/src/hepunits/constants/constants.py
index 8d082f1..b52f06f 100644
--- a/src/hepunits/constants/constants.py
+++ b/src/hepunits/constants/constants.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 """
 Physical and other handy constants
@@ -28,11 +27,36 @@
 # -----------------------------------------------------------------------------
 # Import statements
 # -----------------------------------------------------------------------------
-from __future__ import absolute_import
 
 from math import pi
+from typing import List
+
+from ..units.units import eplus, joule, kelvin, m, mole, s
+
+__all__ = (
+    "m",
+    "s",
+    "eplus",
+    "mole",
+    "joule",
+    "kelvin",
+    "c_light",
+    "c_light_sq",
+    "pi",
+    "two_pi",
+    "half_pi",
+    "pi_sq",
+    "eminus",
+    "e_sq",
+    "Avogadro",
+    "h_Planck",
+    "hbar_Planck",
+    "hbar",
+    "hbarc",
+    "hbarc_sq",
+    "k_Boltzmann",
+)
 
-from ..units.units import m, s, eplus, mole, joule, kelvin
 
 # -----------------------------------------------------------------------------
 # Mathematical constants
@@ -69,3 +93,7 @@
 
 # Boltzmann constant (exact value, taken from PDG 2020)
 k_Boltzmann = 1.380649e-23 * joule / kelvin
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/src/hepunits/constants/py.typed b/src/hepunits/constants/py.typed
deleted file mode 100644
index e69de29..0000000
diff --git a/src/hepunits/units/__init__.py b/src/hepunits/units/__init__.py
index b47a232..b8b11ef 100644
--- a/src/hepunits/units/__init__.py
+++ b/src/hepunits/units/__init__.py
@@ -1,5 +1,452 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 
-from .prefixes import *
-from .units import *
+from typing import List
+
+from . import prefixes, units
+from .prefixes import (
+    atto,
+    centi,
+    deca,
+    deci,
+    exa,
+    exbi,
+    femto,
+    gibi,
+    giga,
+    googol,
+    hecto,
+    kibi,
+    kilo,
+    mebi,
+    mega,
+    micro,
+    milli,
+    nano,
+    pebi,
+    peta,
+    pico,
+    tebi,
+    tera,
+    yobi,
+    yocto,
+    yotta,
+    zebi,
+    zepto,
+    zetta,
+)
+from .units import (
+    GW,
+    MW,
+    A,
+    Bq,
+    Ci,
+    EeV,
+    GBq,
+    GeV,
+    GHz,
+    Gy,
+    Hz,
+    J,
+    MBq,
+    MeV,
+    MGy,
+    MHz,
+    N,
+    Pa,
+    PeV,
+    Sv,
+    TeV,
+    THz,
+    W,
+    ZeV,
+    ab,
+    ampere,
+    angstrom,
+    atmosphere,
+    attobarn,
+    attosecond,
+    bar,
+    barn,
+    becquerel,
+    candela,
+    cd,
+    centimeter,
+    centimeter2,
+    centimeter3,
+    cm,
+    cm2,
+    cm3,
+    coulomb,
+    curie,
+    d,
+    day,
+    deg,
+    degree,
+    dyne,
+    e_SI,
+    electronvolt,
+    eplus,
+    erg,
+    eV,
+    exaelectronvolt,
+    farad,
+    fb,
+    femtobarn,
+    femtometer,
+    femtosecond,
+    fermi,
+    fm,
+    fm2,
+    fm3,
+    fs,
+    g,
+    gauss,
+    gigabecquerel,
+    gigaelectronvolt,
+    gigahertz,
+    gram,
+    gray,
+    h,
+    henry,
+    hertz,
+    hour,
+    invab,
+    invfb,
+    invmb,
+    invnb,
+    invpb,
+    invub,
+    joule,
+    kBq,
+    kelvin,
+    keV,
+    kg,
+    kGy,
+    kHz,
+    kilobecquerel,
+    kiloelectronvolt,
+    kilogauss,
+    kilogram,
+    kilogray,
+    kilohertz,
+    kilometer,
+    kilometer2,
+    kilometer3,
+    kilovolt,
+    km,
+    km2,
+    km3,
+    kW,
+    lumen,
+    lux,
+    m,
+    m2,
+    m3,
+    mb,
+    mCi,
+    megabecquerel,
+    megaelectronvolt,
+    megagray,
+    megahertz,
+    megavolt,
+    meter,
+    meter2,
+    meter3,
+    mg,
+    mGy,
+    microampere,
+    microbarn,
+    microcurie,
+    microfarad,
+    microgray,
+    micrometer,
+    micron,
+    microsecond,
+    milliampere,
+    millibarn,
+    millicurie,
+    millifarad,
+    milligram,
+    milligray,
+    millimeter,
+    millimeter2,
+    millimeter3,
+    milliradian,
+    millisecond,
+    minute,
+    mm,
+    mm2,
+    mm3,
+    mol,
+    mole,
+    mrad,
+    ms,
+    nanoampere,
+    nanobarn,
+    nanocurie,
+    nanofarad,
+    nanometer,
+    nanosecond,
+    nb,
+    nCi,
+    newton,
+    ns,
+    ohm,
+    pascal,
+    pb,
+    petaelectronvolt,
+    picobarn,
+    picofarad,
+    picosecond,
+    ps,
+    rad,
+    radian,
+    s,
+    second,
+    sievert,
+    sr,
+    steradian,
+    teraelectronvolt,
+    terahertz,
+    tesla,
+    ub,
+    uCi,
+    uGy,
+    us,
+    volt,
+    watt,
+    weber,
+    y,
+    year,
+    yoctosecond,
+    ys,
+    zeptosecond,
+    zettaelectronvolt,
+    zs,
+)
+
+__all__ = (
+    "prefixes",
+    "units",
+    "atto",
+    "centi",
+    "deca",
+    "deci",
+    "exa",
+    "exbi",
+    "femto",
+    "gibi",
+    "giga",
+    "googol",
+    "hecto",
+    "kibi",
+    "kilo",
+    "mebi",
+    "mega",
+    "micro",
+    "milli",
+    "nano",
+    "pebi",
+    "peta",
+    "pico",
+    "tebi",
+    "tera",
+    "yobi",
+    "yocto",
+    "yotta",
+    "zebi",
+    "zepto",
+    "zetta",
+    "A",
+    "Bq",
+    "Ci",
+    "EeV",
+    "GBq",
+    "GHz",
+    "GW",
+    "GeV",
+    "Gy",
+    "Hz",
+    "J",
+    "MBq",
+    "MGy",
+    "MHz",
+    "MW",
+    "MeV",
+    "N",
+    "Pa",
+    "PeV",
+    "Sv",
+    "THz",
+    "TeV",
+    "W",
+    "ZeV",
+    "ab",
+    "ampere",
+    "angstrom",
+    "atmosphere",
+    "attobarn",
+    "attosecond",
+    "bar",
+    "barn",
+    "becquerel",
+    "candela",
+    "cd",
+    "centimeter",
+    "centimeter2",
+    "centimeter3",
+    "cm",
+    "cm2",
+    "cm3",
+    "coulomb",
+    "curie",
+    "d",
+    "day",
+    "deg",
+    "degree",
+    "dyne",
+    "eV",
+    "e_SI",
+    "electronvolt",
+    "eplus",
+    "erg",
+    "exaelectronvolt",
+    "farad",
+    "fb",
+    "femtobarn",
+    "femtometer",
+    "femtosecond",
+    "fermi",
+    "fm",
+    "fm2",
+    "fm3",
+    "fs",
+    "g",
+    "gauss",
+    "gigabecquerel",
+    "gigaelectronvolt",
+    "gigahertz",
+    "gram",
+    "gray",
+    "h",
+    "henry",
+    "hertz",
+    "hour",
+    "invab",
+    "invfb",
+    "invmb",
+    "invnb",
+    "invpb",
+    "invub",
+    "joule",
+    "kBq",
+    "kGy",
+    "kHz",
+    "kW",
+    "keV",
+    "kelvin",
+    "kg",
+    "kilobecquerel",
+    "kiloelectronvolt",
+    "kilogauss",
+    "kilogram",
+    "kilogray",
+    "kilohertz",
+    "kilometer",
+    "kilometer2",
+    "kilometer3",
+    "kilovolt",
+    "km",
+    "km2",
+    "km3",
+    "lumen",
+    "lux",
+    "m",
+    "m2",
+    "m3",
+    "mCi",
+    "mGy",
+    "mb",
+    "megabecquerel",
+    "megaelectronvolt",
+    "megagray",
+    "megahertz",
+    "megavolt",
+    "meter",
+    "meter2",
+    "meter3",
+    "mg",
+    "microampere",
+    "microbarn",
+    "microcurie",
+    "microfarad",
+    "microgray",
+    "micrometer",
+    "micron",
+    "microsecond",
+    "milliampere",
+    "millibarn",
+    "millicurie",
+    "millifarad",
+    "milligram",
+    "milligray",
+    "millimeter",
+    "millimeter2",
+    "millimeter3",
+    "milliradian",
+    "millisecond",
+    "minute",
+    "mm",
+    "mm2",
+    "mm3",
+    "mol",
+    "mole",
+    "mrad",
+    "ms",
+    "nCi",
+    "nanoampere",
+    "nanobarn",
+    "nanocurie",
+    "nanofarad",
+    "nanometer",
+    "nanosecond",
+    "nb",
+    "newton",
+    "ns",
+    "ohm",
+    "pascal",
+    "pb",
+    "petaelectronvolt",
+    "picobarn",
+    "picofarad",
+    "picosecond",
+    "ps",
+    "rad",
+    "radian",
+    "s",
+    "second",
+    "sievert",
+    "sr",
+    "steradian",
+    "teraelectronvolt",
+    "terahertz",
+    "tesla",
+    "uCi",
+    "uGy",
+    "ub",
+    "us",
+    "volt",
+    "watt",
+    "weber",
+    "y",
+    "year",
+    "yoctosecond",
+    "ys",
+    "zeptosecond",
+    "zettaelectronvolt",
+    "zs",
+)
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/src/hepunits/units/prefixes.py b/src/hepunits/units/prefixes.py
index a52933c..c85b346 100644
--- a/src/hepunits/units/prefixes.py
+++ b/src/hepunits/units/prefixes.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 """
 Common unit prefixes
@@ -15,9 +14,44 @@
 .. [Binary_prefixes] https://en.wikipedia.org/wiki/Unit_prefix#Binary_prefixes.
 """
 
+__all__ = (
+    "atto",
+    "centi",
+    "deca",
+    "deci",
+    "exa",
+    "exbi",
+    "femto",
+    "gibi",
+    "giga",
+    "googol",
+    "hecto",
+    "kibi",
+    "kilo",
+    "mebi",
+    "mega",
+    "micro",
+    "milli",
+    "nano",
+    "pebi",
+    "peta",
+    "pico",
+    "tebi",
+    "tera",
+    "yobi",
+    "yocto",
+    "yotta",
+    "zebi",
+    "zepto",
+    "zetta",
+)
+
+
 # -----------------------------------------------------------------------------
 # SI prefixes
 # -----------------------------------------------------------------------------
+from typing import List
+
 yotta = 1.0e24
 zetta = 1.0e21
 exa = 1.0e18
@@ -55,3 +89,7 @@
 # Miscellaneous prefixes
 # -----------------------------------------------------------------------------
 googol = 1.0e100
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/src/hepunits/units/py.typed b/src/hepunits/units/py.typed
deleted file mode 100644
index e69de29..0000000
diff --git a/src/hepunits/units/units.py b/src/hepunits/units/units.py
index fd44b66..d8aa4f7 100644
--- a/src/hepunits/units/units.py
+++ b/src/hepunits/units/units.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 
 """
@@ -67,9 +66,9 @@
 .. [SI] http://www.physics.nist.gov/cuu/Units/index.html.
 """
 
-from __future__ import absolute_import
 
-from math import pi
+from math import pi as _pi
+from typing import List
 
 from . import prefixes as _pre
 
@@ -250,7 +249,7 @@
 milliradian = _pre.milli * radian
 mrad = milliradian
 
-degree = (pi / 180.0) * radian
+degree = (_pi / 180.0) * radian
 
 deg = degree
 
@@ -405,3 +404,198 @@
 sievert = joule / kilogram
 
 Sv = sievert
+
+__all__ = (
+    "A",
+    "Bq",
+    "Ci",
+    "EeV",
+    "GBq",
+    "GHz",
+    "GW",
+    "GeV",
+    "Gy",
+    "Hz",
+    "J",
+    "MBq",
+    "MGy",
+    "MHz",
+    "MW",
+    "MeV",
+    "N",
+    "Pa",
+    "PeV",
+    "Sv",
+    "THz",
+    "TeV",
+    "W",
+    "ZeV",
+    "ab",
+    "ampere",
+    "angstrom",
+    "atmosphere",
+    "attobarn",
+    "attosecond",
+    "bar",
+    "barn",
+    "becquerel",
+    "candela",
+    "cd",
+    "centimeter",
+    "centimeter2",
+    "centimeter3",
+    "cm",
+    "cm2",
+    "cm3",
+    "coulomb",
+    "curie",
+    "d",
+    "day",
+    "deg",
+    "degree",
+    "dyne",
+    "eV",
+    "e_SI",
+    "electronvolt",
+    "eplus",
+    "erg",
+    "exaelectronvolt",
+    "farad",
+    "fb",
+    "femtobarn",
+    "femtometer",
+    "femtosecond",
+    "fermi",
+    "fm",
+    "fm2",
+    "fm3",
+    "fs",
+    "g",
+    "gauss",
+    "gigabecquerel",
+    "gigaelectronvolt",
+    "gigahertz",
+    "gram",
+    "gray",
+    "h",
+    "henry",
+    "hertz",
+    "hour",
+    "invab",
+    "invfb",
+    "invmb",
+    "invnb",
+    "invpb",
+    "invub",
+    "joule",
+    "kBq",
+    "kGy",
+    "kHz",
+    "kW",
+    "keV",
+    "kelvin",
+    "kg",
+    "kilobecquerel",
+    "kiloelectronvolt",
+    "kilogauss",
+    "kilogram",
+    "kilogray",
+    "kilohertz",
+    "kilometer",
+    "kilometer2",
+    "kilometer3",
+    "kilovolt",
+    "km",
+    "km2",
+    "km3",
+    "lumen",
+    "lux",
+    "m",
+    "m2",
+    "m3",
+    "mCi",
+    "mGy",
+    "mb",
+    "megabecquerel",
+    "megaelectronvolt",
+    "megagray",
+    "megahertz",
+    "megavolt",
+    "meter",
+    "meter2",
+    "meter3",
+    "mg",
+    "microampere",
+    "microbarn",
+    "microcurie",
+    "microfarad",
+    "microgray",
+    "micrometer",
+    "micron",
+    "microsecond",
+    "milliampere",
+    "millibarn",
+    "millicurie",
+    "millifarad",
+    "milligram",
+    "milligray",
+    "millimeter",
+    "millimeter2",
+    "millimeter3",
+    "milliradian",
+    "millisecond",
+    "minute",
+    "mm",
+    "mm2",
+    "mm3",
+    "mol",
+    "mole",
+    "mrad",
+    "ms",
+    "nCi",
+    "nanoampere",
+    "nanobarn",
+    "nanocurie",
+    "nanofarad",
+    "nanometer",
+    "nanosecond",
+    "nb",
+    "newton",
+    "ns",
+    "ohm",
+    "pascal",
+    "pb",
+    "petaelectronvolt",
+    "picobarn",
+    "picofarad",
+    "picosecond",
+    "ps",
+    "rad",
+    "radian",
+    "s",
+    "second",
+    "sievert",
+    "sr",
+    "steradian",
+    "teraelectronvolt",
+    "terahertz",
+    "tesla",
+    "uCi",
+    "uGy",
+    "ub",
+    "us",
+    "volt",
+    "watt",
+    "weber",
+    "y",
+    "year",
+    "yoctosecond",
+    "ys",
+    "zeptosecond",
+    "zettaelectronvolt",
+    "zs",
+)
+
+
+def __dir__() -> List[str]:
+    return list(__all__)
diff --git a/tests/constants/test_constants.py b/tests/constants/test_constants.py
index 9b78310..b9d7bb9 100644
--- a/tests/constants/test_constants.py
+++ b/tests/constants/test_constants.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 """
 Tests for the hepunits.constants.constants module.
@@ -7,8 +6,8 @@
 
 from pytest import approx
 
-from hepunits import eV, nanometer, s, THz
 from hepunits import *
+from hepunits import THz, eV, nanometer, s
 
 
 def test_constants():
diff --git a/tests/test_missing_all.py b/tests/test_missing_all.py
new file mode 100644
index 0000000..8d68208
--- /dev/null
+++ b/tests/test_missing_all.py
@@ -0,0 +1,53 @@
+import sys
+
+import pytest
+
+import hepunits
+
+
+def filter_module(item: str) -> bool:
+    if item == "__version__":
+        return True
+    if item.startswith("_"):
+        return False
+    if item in {"List"}:
+        return False
+    return True
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 7), reason="Python 3.7+ added __dir__ support"
+)
+@pytest.mark.parametrize(
+    "module",
+    (
+        hepunits,
+        hepunits.units,
+        hepunits.constants,
+        hepunits.constants.constants,
+        hepunits.units.prefixes,
+        hepunits.units.units,
+    ),
+)
+def test_missing_all(module):
+    assert set(dir(module)) == set(module.__all__)
+
+    full_module = {it for it in module.__dict__ if filter_module(it)}
+    assert full_module == set(module.__all__)
+
+
+def test_exported():
+    expr = set(hepunits.units.__all__) - (set(hepunits.__all__) | {"prefixes"})
+    assert not expr
+
+    expr = set(hepunits.constants.__all__) - set(hepunits.__all__)
+    assert not expr
+
+    expr = set(hepunits.constants.constants.__all__) - set(hepunits.constants.__all__)
+    assert not expr
+
+    expr = set(hepunits.units.prefixes.__all__) - set(hepunits.units.__all__)
+    assert not expr
+
+    expr = set(hepunits.units.units.__all__) - set(hepunits.units.__all__)
+    assert not expr
diff --git a/tests/units/test_prefixes.py b/tests/units/test_prefixes.py
index e2bdb6b..a5e253f 100644
--- a/tests/units/test_prefixes.py
+++ b/tests/units/test_prefixes.py
@@ -1,15 +1,14 @@
 #!/usr/bin/env python
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 """
 Tests for the hepunits.units.prefixes module.
 """
 
-from pytest import approx
-
 from math import log
 
-from hepunits import mega, micro, yotta, yocto, kibi, tebi
+from pytest import approx
+
+from hepunits import kibi, mega, micro, tebi, yocto, yotta
 
 
 def test_prefixes_e6():
diff --git a/tests/units/test_units.py b/tests/units/test_units.py
index cb0cb85..e4b6b82 100644
--- a/tests/units/test_units.py
+++ b/tests/units/test_units.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# -*- coding: utf-8 -*-
 # Licensed under a 3-clause BSD style license, see LICENSE.
 """
 Tests for the hepunits.units.units module.