diff --git a/Makefile b/Makefile
index bd4bb88..31c68ae 100644
--- a/Makefile
+++ b/Makefile
@@ -4,6 +4,7 @@ clean:
 	rm -rf .pytest_cache
 	rm -rf build
 	rm -rf dist
+	rm -rf downloads
 
 pypi: clean
 	python setup.py sdist
@@ -12,10 +13,12 @@ pypi: clean
 
 install:
 	python -m pip install --upgrade pip
-	python -m pip install -e .
+	python -m pip install -e ".[dev]"
 
 serve:
 	python -m bulk text cluestarred.csv
 
 test:
 	pytest
+
+check: clean test clean
\ No newline at end of file
diff --git a/bulk/__main__.py b/bulk/__main__.py
index b561430..d5770fd 100644
--- a/bulk/__main__.py
+++ b/bulk/__main__.py
@@ -17,8 +17,10 @@ app = typer.Typer(
 app.add_typer(util_app, name="util")
 
 
+
 @app.command("version")
 def version():
+    """Prints the version."""
     print("0.1.0")
 
 
diff --git a/bulk/_bokeh_utils.py b/bulk/_bokeh_utils.py
index 5276d85..67dd7f5 100644
--- a/bulk/_bokeh_utils.py
+++ b/bulk/_bokeh_utils.py
@@ -20,6 +20,9 @@ def get_color_mapping(df: pd.DataFrame) -> Tuple[Optional[bokeh.transform.transf
         all_values = list(df["color"].dropna().unique())
         if len(all_values) == 2:
             all_values.extend([""])
+        elif len(all_values) > len(Category10) + 2:
+            raise ValueError(f"Too many classes defined, the limit for visualisation is {len(Category10) + 2}. "
+                             f"Got {len(all_values)}.")
         mapper = factor_cmap(
             field_name="color",
             palette=Category10[len(all_values)],
diff --git a/bulk/download.py b/bulk/download.py
new file mode 100644
index 0000000..61337a3
--- /dev/null
+++ b/bulk/download.py
@@ -0,0 +1,55 @@
+import shutil
+import pathlib
+import pandas as pd
+import tarfile
+import urllib.request
+import typer
+
+
+app = typer.Typer(
+    name="download",
+    add_completion=False,
+    help="Download datasets.",
+    no_args_is_help=True,
+)
+
+
+@app.command("tinyplanet")
+def tinyplanet(force: bool = typer.Option(False, help="Force the download", is_flag=True)):
+    """
+    Download the tiny planet dataset.
+
+    The dataset contains satellite images to track the human footprint in the Amazon rainforest.
+    
+    This dataset was uses the same dataresource as the fast.ai project, found here:
+    https://docs.fast.ai/data.external.html
+
+    It is a small subset of a dataset that was originally found as part of a Kaggle competition, found here:
+    https://www.kaggle.com/c/planet-understanding-the-amazon-from-space
+    """
+    src = pathlib.Path("downloads/tinyplanet/tinyplanet.tgz")
+    if not force and src.parent.exists():
+        print("The tinyplanet dataset already exists")
+        raise typer.Exit(1)
+    src.parent.mkdir(exist_ok=True, parents=True)
+    dst = pathlib.Path("downloads/tinyplanet")
+    
+    # Download and untar
+    urllib.request.urlretrieve("https://s3.amazonaws.com/fast-ai-sample/planet_tiny.tgz", str(src))
+    with tarfile.open(str(src), 'r:gz') as tar:
+        tar.extractall(str(dst))
+    src.unlink()
+
+    # Move files into nice positions
+    glob = pathlib.Path("downloads/tinyplanet/planet_tiny/train").glob("*.jpg")
+    pathlib.Path("downloads/tinyplanet/images").mkdir(exist_ok=True, parents=True)
+    for file in glob:
+        file.rename(f"downloads/tinyplanet/images/{file.name}")
+
+    # Move the labels file 
+    (pd.read_csv("downloads/tinyplanet/planet_tiny/labels.csv")
+      .assign(image=lambda d: d['image_name'].str.replace("train_", ""))
+      .drop(columns=["image_name"])
+      .to_csv("downloads/tinyplanet/labels.csv", index=False))
+
+    shutil.rmtree("downloads/tinyplanet/planet_tiny")
diff --git a/bulk/util.py b/bulk/util.py
index 66519af..2dcee54 100644
--- a/bulk/util.py
+++ b/bulk/util.py
@@ -1,15 +1,17 @@
-from typing import List
 import pathlib 
+from typing import List
 
 import typer
 import pandas as pd
+from bulk.download import app as download_app
 
 app = typer.Typer(
     name="util",
     add_completion=False,
-    help="Utilities for data.",
+    help="Extra utilities.",
     no_args_is_help=True,
 )
+app.add_typer(download_app, name="download")
 
 
 @app.command("concat")

diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..d2849c3
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,16 @@
+import pathlib 
+from typer.testing import CliRunner
+
+from bulk.__main__ import app
+
+runner = CliRunner()
+
+
+def test_download_tinyplanet():
+    result = runner.invoke(app, ["util", "download", "tinyplanet"])
+    assert result.exit_code == 0
+    assert pathlib.Path("downloads/tinyplanet").exists()
+
+    # The path exists now, so exit_code needs to be raised
+    result = runner.invoke(app, ["util", "download", "tinyplanet"])
+    assert result.exit_code == 1
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..2b851b4
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,33 @@
+import pandas as pd
+import pytest
+
+from bulk._bokeh_utils import get_color_mapping
+
+MAX_DISCRETE_CLASSES = 10
+
+
+def _int_to_alpha(x: int) -> str:
+    # returns int mapped to char: 0: a, 1: b, 2: c
+    return chr(x + 97)
+
+
+def _create_dummy_df() -> pd.DataFrame:
+    df = pd.DataFrame()
+    df["color"] = [_int_to_alpha(i) for i in range(MAX_DISCRETE_CLASSES)]
+    return df
+
+
+def test_get_color_mapping_raises_error_on_too_many_classes():
+    df = _create_dummy_df()
+    additional_class = pd.DataFrame.from_records([{"color": _int_to_alpha(MAX_DISCRETE_CLASSES + 1)}])
+    df = pd.concat([df, additional_class], axis=0, ignore_index=True)
+    with pytest.raises(ValueError):
+        get_color_mapping(df)
+
+
+def test_get_color_mapping_doesnt_raise_error():
+    df = _create_dummy_df()
+    try:
+        get_color_mapping(df)
+    except ValueError as e:
+        assert False, f"get_color_mapping raised a ValueError: {e}"

Color mapping crashes if too many classes defined
Looks like I crashed the color mapping with too many classes.

The palette could be upped to Category20, though this would still limit the number of classes a user can visualize. Whatever the limit is, there should be an error message with a graceful exit if the user tries to define more. I'd be happy to make a PR!

```Traceback (most recent call last):
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/tornado/web.py", line 1713, in _execute
    result = await result
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bokeh/server/views/doc_handler.py", line 54, in get
    session = await self.get_session()
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bokeh/server/views/session_handler.py", line 144, in get_session
    session = await self.application_context.create_session_if_needed(session_id, self.request, token)
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bokeh/server/contexts.py", line 243, in create_session_if_needed
    self._application.initialize_document(doc)
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bokeh/application/application.py", line 194, in initialize_document
    h.modify_document(doc)
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bokeh/application/handlers/function.py", line 143, in modify_document
    self._func(doc)
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bulk/text.py", line 27, in bkapp
    mapper, df = get_color_mapping(df)
  File ".pyenv/versions/rules-env/lib/python3.8/site-packages/bulk/utils.py", line 25, in get_color_mapping
    palette=Category10[len(all_values)],
KeyError: 16```
tests/test_utils.py::test_get_color_mapping_raises_error_on_too_many_classes
tests/test_utils.py::test_get_color_mapping_doesnt_raise_error