diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 216f9be..71d3e3c 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  - Change CDS keys from `.cdsapirc` file to `.config/eracli.txt` file. This will avoid conflict with e.g. ADS.
  - If a user makes a request without `--splitmonths` they are warned that the behavior will change in the future, and that they have to choose between `--splitmonths False` and `--splitmonths True`.
  - When a request would encounter a Request Too Large error in the CDS API, they are warned, and given a suggestion to use `--splitmonths`.
+ - When a file already exists and would be overwritten, the user is prompted for confirmation. This should prevent accidental overwriting of files. This check can be skipped with the `--overwrite` flag.
  - The earliest valid start year of requests has been updated to 1950.
  - Usage of `--prelimbe` now raises a deprecation warning. It will be deprecated in a future release, as all the back extension years are now included in the main products.
 
diff --git a/era5cli/args/common.py b/era5cli/args/common.py
index 35194b5..73d6c4d 100644
--- a/era5cli/args/common.py
+++ b/era5cli/args/common.py
@@ -27,6 +27,7 @@ def add_common_args(argument_parser: ArgumentParser) -> None:
         --prelimbe,
         --land,
         --area,
+        --overwrite
 
     Args:
         argument_parser: the ArgumentParser that the arguments are added to.
@@ -242,6 +243,22 @@ def add_common_args(argument_parser: ArgumentParser) -> None:
         ),
     )
 
+    argument_parser.add_argument(
+        "--overwrite",
+        action="store_true",
+        default=False,
+        help=textwrap.dedent(
+            """
+            Whether to overwrite existing files or not.
+            Providing the `--overwrite` argument will make
+            era5cli overwrite existing files. By default,
+            you will be prompted if a file already exists, with
+            the question if you want to overwrite it or not.
+
+            """
+        ),
+    )
+
 
 def construct_year_list(args):
     """Make a continous list of years from the startyear and endyear arguments."""
diff --git a/era5cli/args/periods.py b/era5cli/args/periods.py
index d6988fd..a049590 100644
--- a/era5cli/args/periods.py
+++ b/era5cli/args/periods.py
@@ -185,7 +185,6 @@ def set_period_args(args):
             )
         else:
             splitmonths: bool = args.splitmonths
-        print(splitmonths)
 
         statistics: bool = args.statistics
         if statistics:
diff --git a/era5cli/cli.py b/era5cli/cli.py
index 4a2d2c6..8bc6d06 100644
--- a/era5cli/cli.py
+++ b/era5cli/cli.py
@@ -69,6 +69,7 @@ def _execute(input_args: argparse.Namespace) -> True:
         merge=input_args.merge,
         prelimbe=input_args.prelimbe,
         land=input_args.land,
+        overwrite=input_args.overwrite,
     )
     era5.fetch(dryrun=input_args.dryrun)
     return True
diff --git a/era5cli/fetch.py b/era5cli/fetch.py
index 02d13ce..9f76188 100644
--- a/era5cli/fetch.py
+++ b/era5cli/fetch.py
@@ -86,6 +86,12 @@ class Fetch:
             Note that the ERA5-Land dataset starts in 1981.
             `land = True` is incompatible with the use of
             `prelimbe = True` and `ensemble = True`.
+        overwrite: bool
+            Whether to overwrite existing files or not.
+            Setting `overwrite = True` will make
+            era5cli overwrite existing files. By default,
+            you will be prompted if a file already exists, with
+            the question if you want to overwrite it or not.
     """
 
     def __init__(
@@ -108,6 +114,7 @@ class Fetch:
         threads=None,
         prelimbe=False,
         land=False,
+        overwrite=False,
     ):
         """Initialization of Fetch class."""
         self._get_login()  # Get login info from config file.
@@ -166,6 +173,8 @@ class Fetch:
         self.land = land
         """bool: Whether to download from the ERA5-Land
         dataset."""
+        self.overwrite = overwrite
+        """bool: Whether to overwrite existing files."""
 
         if self.merge and self.splitmonths:
             raise ValueError(
@@ -197,6 +206,9 @@ class Fetch:
             )
 
     def _get_login(self):
+        # First check if the config exists, and guide the user if it does not.
+        key_management.check_era5cli_config()
+        # Only then load the keys (as they should be there now).
         self.url, self.key = key_management.load_era5cli_config()
 
     def fetch(self, dryrun=False):
@@ -271,11 +283,12 @@ class Fetch:
         outputfiles = [
             self._define_outputfilename(var, self.years) for var in self.variables
         ]
+        if not self.overwrite:
+            era5cli.utils.assert_outputfiles_not_exist(outputfiles)
+
         years = len(outputfiles) * [self.years]
-        if not self.threads:
-            pool = Pool()
-        else:
-            pool = Pool(nodes=self.threads)
+
+        pool = Pool(nodes=self.threads) if self.threads else Pool()
         pool.map(self._getdata, self.variables, years, outputfiles)
 
     def _split_variable_yr(self):
@@ -285,7 +298,12 @@ class Fetch:
         for var in self.variables:
             outputfiles += [self._define_outputfilename(var, [yr]) for yr in self.years]
             variables += len(self.years) * [var]
+
+        if not self.overwrite:
+            era5cli.utils.assert_outputfiles_not_exist(outputfiles)
+
         years = len(self.variables) * self.years
+
         pool = Pool(nodes=self.threads) if self.threads else Pool()
         pool.map(self._getdata, variables, years, outputfiles)
 
@@ -304,6 +322,9 @@ class Fetch:
             years += [year]
             months += [month]
 
+        if not self.overwrite:
+            era5cli.utils.assert_outputfiles_not_exist(outputfiles)
+
         pool = Pool(nodes=self.threads) if self.threads else Pool()
         pool.map(self._getdata, variables, years, outputfiles, months)
 
@@ -501,6 +522,7 @@ class Fetch:
     def _getdata(self, variables: list, years: list, outputfile: str, months=None):
         """Fetch variables using cds api call."""
         name, request = self._build_request(variables, years, months)
+
         if self.dryrun:
             print(name, request, outputfile)
         else:
diff --git a/era5cli/utils.py b/era5cli/utils.py
index 2f8545a..37650a8 100644
--- a/era5cli/utils.py
+++ b/era5cli/utils.py
@@ -4,6 +4,7 @@ import datetime
 import shutil
 import textwrap
 from pathlib import Path
+from typing import List
 import prettytable
 from netCDF4 import Dataset
 import era5cli
@@ -205,3 +206,18 @@ def strtobool(value: str) -> bool:
         "Could not convert string to boolean. Valid inputs are:"
         f"{trues} and {falses} (case insensitive)."
     )
+
+
+def assert_outputfiles_not_exist(outputfiles: List[str]) -> None:
+    """Check if files already exist, and prompt the user if they do."""
+    if any(Path(file).exists() for file in outputfiles):
+        answer = input(
+            "\n  Some filenames already exists in this folder."
+            "\n  Do you want to overwrite them? (Y/N)"
+            "\n  Tip: to skip this flag, use `--overwrite`."
+        )
+        if answer.lower() in ["n", "no", "nope"]:
+            raise FileExistsError(
+                "\n  One or more files already exist in this folder."
+                "\n  Please remove them, or change to a different folder to continue"
+            )

diff --git a/tests/test_fetch.py b/tests/test_fetch.py
index 34b67f1..97b21d4 100644
--- a/tests/test_fetch.py
+++ b/tests/test_fetch.py
@@ -1,5 +1,6 @@
 """Tests for era5cli Fetch class."""
 
+import pathlib
 import unittest.mock as mock
 import pytest
 from era5cli import _request_size
@@ -23,6 +24,14 @@ ALL_MONTHS = ["01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11",
 # fmt: on
 
 
+@pytest.fixture(scope="module", autouse=True)
+def my_thing_mock():
+    with mock.patch(
+        "era5cli.fetch.key_management.check_era5cli_config", autospec=True
+    ) as _fixture:
+        yield _fixture
+
+
 def initialize(
     outputformat="netcdf",
     merge=False,
@@ -41,6 +50,7 @@ def initialize(
     prelimbe=False,
     land=False,
     splitmonths=False,
+    overwrite=False,
 ):
     with mock.patch(
         "era5cli.fetch.key_management.load_era5cli_config",
@@ -66,6 +76,7 @@ def initialize(
             prelimbe=prelimbe,
             land=land,
             splitmonths=splitmonths,
+            overwrite=overwrite,
         )
 
 
@@ -643,3 +654,21 @@ def test_area():
     with pytest.raises(ValueError):
         era5 = initialize(area=[-180, 180, -90])
         era5._build_request("total_precipitation", [2008])
+
+
+def test_file_exists():
+    with mock.patch.object(pathlib.Path, "exists", return_value=True):
+        era5 = initialize()
+
+        with mock.patch("builtins.input", return_value="Y"):
+            era5.fetch(dryrun=True)
+
+        with mock.patch("builtins.input", return_value="N"):
+            with pytest.raises(FileExistsError):
+                era5.fetch(dryrun=True)
+
+
+def test_overwrite():
+    with mock.patch.object(pathlib.Path, "exists", return_value=True):
+        era5 = initialize(overwrite=True)
+        era5.fetch(dryrun=True)
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 8f348d7..859fa77 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -7,6 +7,14 @@ import pytest
 from era5cli.cli import main
 
 
+@pytest.fixture(scope="module", autouse=True)
+def my_thing_mock():
+    with mock.patch(
+        "era5cli.fetch.key_management.check_era5cli_config", autospec=True
+    ) as _fixture:
+        yield _fixture
+
+
 # combine calls with result and possible warning message
 call_result = [
     {

An option for overwriting the existing file and checking its size
Implement an option for checking the existing file in the downloading directory and its size. 
to find out the size, it might be useful to have a look at:
**Use MARS "list" verb to find out the size of your request**
https://confluence.ecmwf.int/pages/viewpage.action?pageId=77223119#HRES:Atmospheric(oper),Modellevel(ml),Forecast(fc)-UseMARS%22list%22verbtofindoutthesizeofyourrequest

tests/test_fetch.py::test_init tests/test_fetch.py::test_fetch_nodryrun tests/test_fetch.py::test_fetch_dryrun tests/test_fetch.py::test_extension tests/test_fetch.py::test_define_outputfilename tests/test_fetch.py::test_number_outputfiles[variables0-years0-False-False-False-6] tests/test_fetch.py::test_number_outputfiles[variables1-years1-True-False-False-2] tests/test_fetch.py::test_number_outputfiles[variables2-years2-False-True-False-6] tests/test_fetch.py::test_number_outputfiles[variables3-years3-False-True-True-72] tests/test_fetch.py::test_number_outputfiles[variables4-years4-False-False-False-2] tests/test_fetch.py::test_number_outputfiles[variables5-years5-False-False-False-3] tests/test_fetch.py::test_product_type tests/test_fetch.py::test_check_levels tests/test_fetch.py::test_check_variable tests/test_fetch.py::test_build_name tests/test_fetch.py::test_build_request tests/test_fetch.py::test_incompatible_options tests/test_fetch.py::test_area tests/test_fetch.py::test_file_exists tests/test_fetch.py::test_overwrite
tests/test_integration.py::test_main[era5cli