diff --git a/.scripts/tests-e2e.sh b/.scripts/tests-e2e.sh
index 725812e..4ed0bbe 100755
--- a/.scripts/tests-e2e.sh
+++ b/.scripts/tests-e2e.sh
@@ -128,6 +128,19 @@ assertSuccess "ls $HOME/kosmorro/export/document.pdf"
 assertSuccess "$KOSMORRO_COMMAND --position=\"50.5876;3.0624\" -d 2020-01-27 --format=pdf -o $HOME/kosmorro/export/document-no-graph.pdf --no-graph"
 assertSuccess "ls $HOME/kosmorro/export/document-no-graph.pdf"
 
+# If format argument is given, use it even if it conflicts with file extension
+assertSuccess "$KOSMORRO_COMMAND --position=\"50.5876;3.0624\" -d 2020-01-27 --format=json -o $HOME/kosmorro/export/txt-document.txt"
+assertSuccess "ls $HOME/kosmorro/export/txt-document.txt"
+
+assertSuccess "$KOSMORRO_COMMAND --position=\"50.5876;3.0624\" -d 2020-01-27 -o $HOME/kosmorro/export/txt-document.txt"
+assertSuccess "ls $HOME/kosmorro/export/txt-document.txt"
+
+assertSuccess "$KOSMORRO_COMMAND --position=\"50.5876;3.0624\" -d 2020-01-27 -o $HOME/kosmorro/export/json-document.json"
+assertSuccess "ls $HOME/kosmorro/export/json-document.json"
+
+assertSuccess "$KOSMORRO_COMMAND --position=\"50.5876;3.0624\" -d 2020-01-27 -o $HOME/kosmorro/export/pdf-document.pdf"
+assertSuccess "ls $HOME/kosmorro/export/pdf-document.pdf"
+
 # man page
 assertSuccess "man --pager=cat kosmorro"
 
diff --git a/_kosmorro/exceptions.py b/_kosmorro/exceptions.py
index 88ae9b8..4c36c3e 100644
--- a/_kosmorro/exceptions.py
+++ b/_kosmorro/exceptions.py
@@ -39,6 +39,19 @@ class OutOfRangeDateError(RuntimeError):
         )
 
 
+class InvalidOutputFormatError(RuntimeError):
+    def __init__(self, output_format: str, accepted_extensions: [str]):
+        super().__init__()
+        self.output_format = output_format
+        self.accepted_extensions = accepted_extensions
+        self.msg = _(
+            "Invalid output format: {output_format}. Output file must end with: {accepted_extensions}"
+        ).format(
+            output_format=output_format,
+            accepted_extensions=", ".join(accepted_extensions),
+        )
+
+
 class CompileError(RuntimeError):
     def __init__(self, msg):
         super().__init__()
diff --git a/_kosmorro/locales/messages.pot b/_kosmorro/locales/messages.pot
index 51395ea..2938de2 100644
--- a/_kosmorro/locales/messages.pot
+++ b/_kosmorro/locales/messages.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: kosmorro 0.10.1\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2021-08-10 20:23+0200\n"
+"POT-Creation-Date: 2021-08-24 17:06-0500\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -116,6 +116,12 @@ msgstr ""
 msgid "The date must be between {minimum_date} and {maximum_date}"
 msgstr ""
 
+#: _kosmorro/exceptions.py:47
+msgid ""
+"Invalid output format: {output_format}. Output file must end with: "
+"{accepted_extensions}"
+msgstr ""
+
 #: _kosmorro/geolocation.py:14
 #, python-format
 msgid "The given position (%s) is not valid."
@@ -125,104 +131,106 @@ msgstr ""
 msgid "The given Plus Code seems to be a short code, please provide a full code."
 msgstr ""
 
-#: _kosmorro/main.py:58
+#: _kosmorro/main.py:73
 msgid ""
 "Save the planet and paper!\n"
 "Consider printing your PDF document only if really necessary, and use the"
 " other side of the sheet."
 msgstr ""
 
-#: _kosmorro/main.py:67
+#: _kosmorro/main.py:82
 msgid ""
 "PDF output will not contain the ephemerides, because you didn't provide "
 "the observation coordinates."
 msgstr ""
 
-#: _kosmorro/main.py:112
+#: _kosmorro/main.py:132
 msgid "The file could not be saved in \"{path}\": {error}"
 msgstr ""
 
-#: _kosmorro/main.py:126
+#: _kosmorro/main.py:146
 msgid "Please provide a file path to export in this format (--output)."
 msgstr ""
 
-#: _kosmorro/main.py:159
+#: _kosmorro/main.py:179
 msgid "Moon phase can only be displayed between {min_date} and {max_date}"
 msgstr ""
 
-#: _kosmorro/main.py:198
+#: _kosmorro/main.py:228
 msgid "Running on Python {python_version} with Kosmorrolib v{kosmorrolib_version}"
 msgstr ""
 
-#: _kosmorro/main.py:208
+#: _kosmorro/main.py:238
 msgid "Do you really want to clear Kosmorro's cache? [yN] "
 msgstr ""
 
-#: _kosmorro/main.py:216
+#: _kosmorro/main.py:246
 msgid "Incorrect answer, cache not cleared."
 msgstr ""
 
-#: _kosmorro/main.py:226
+#: _kosmorro/main.py:256
 msgid ""
 "Compute the ephemerides and the events for a given date and a given "
 "position on Earth."
 msgstr ""
 
-#: _kosmorro/main.py:229
+#: _kosmorro/main.py:259
 msgid ""
 "By default, only the events will be computed for today ({date}).\n"
 "To compute also the ephemerides, latitude and longitude arguments are "
 "needed."
 msgstr ""
 
-#: _kosmorro/main.py:243
+#: _kosmorro/main.py:273
 msgid "Show the program version"
 msgstr ""
 
-#: _kosmorro/main.py:251
+#: _kosmorro/main.py:281
 msgid "Delete all the files from Kosmorro's cache."
 msgstr ""
 
-#: _kosmorro/main.py:259
-msgid "The format to output the information to"
+#: _kosmorro/main.py:289
+msgid ""
+"The format to output the information to. If not provided, the output "
+"format will be inferred from the file extension of the output file."
 msgstr ""
 
-#: _kosmorro/main.py:266
+#: _kosmorro/main.py:299
 msgid ""
 "The observer's position on Earth, in the \"{latitude},{longitude}\" "
 "format.Can also be set in the KOSMORRO_POSITION environment variable."
 msgstr ""
 
-#: _kosmorro/main.py:276
+#: _kosmorro/main.py:309
 msgid ""
 "The date for which the ephemerides must be calculated. Can be in the "
 "YYYY-MM-DD format or an interval in the \"[+-]YyMmDd\" format (with Y, M,"
 " and D numbers). Defaults to today ({default_date})."
 msgstr ""
 
-#: _kosmorro/main.py:287
+#: _kosmorro/main.py:320
 msgid ""
 "The timezone to display the hours in (e.g. 2 for UTC+2 or -3 for UTC-3). "
 "Can also be set in the KOSMORRO_TIMEZONE environment variable."
 msgstr ""
 
-#: _kosmorro/main.py:296
+#: _kosmorro/main.py:329
 msgid "Disable the colors in the console."
 msgstr ""
 
-#: _kosmorro/main.py:303
+#: _kosmorro/main.py:336
 msgid ""
 "A file to export the output to. If not given, the standard output is "
 "used. This argument is needed for PDF format."
 msgstr ""
 
-#: _kosmorro/main.py:312
+#: _kosmorro/main.py:345
 msgid ""
 "Do not generate a graph to represent the rise and set times in the PDF "
 "format."
 msgstr ""
 
-#: _kosmorro/main.py:320
+#: _kosmorro/main.py:353
 msgid "Show debugging messages"
 msgstr ""
 
diff --git a/_kosmorro/main.py b/_kosmorro/main.py
index 56c5c52..1716e2f 100644
--- a/_kosmorro/main.py
+++ b/_kosmorro/main.py
@@ -20,6 +20,7 @@ import argparse
 import locale
 import re
 import sys
+import os.path
 
 from kosmorrolib import Position, get_ephemerides, get_events, get_moon_phase
 from kosmorrolib.__version__ import __version__ as kosmorrolib_version
@@ -31,7 +32,11 @@ from . import dumper, environment, debug
 from .date import parse_date
 from .geolocation import get_position
 from .__version__ import __version__ as kosmorro_version
-from .exceptions import UnavailableFeatureError, OutOfRangeDateError as DateRangeError
+from .exceptions import (
+    InvalidOutputFormatError,
+    UnavailableFeatureError,
+    OutOfRangeDateError as DateRangeError,
+)
 from _kosmorro.i18n.utils import _, SHORT_DATE_FORMAT
 
 
@@ -53,6 +58,16 @@ def main():
 
     position = get_position(args.position) if args.position not in [None, ""] else None
 
+    # if output format is not specified, try to use output file extension as output format
+    if args.output is not None and output_format is None:
+        file_extension = os.path.splitext(args.output)[-1][1:].lower()
+        if file_extension:
+            output_format = file_extension
+
+    # default to .txt if output format was not given and output file did not have file extension
+    if output_format is None:
+        output_format = "txt"
+
     if output_format == "pdf":
         print(
             _(
@@ -88,6 +103,10 @@ def main():
             args.colors,
             args.show_graph,
         )
+    except InvalidOutputFormatError as error:
+        print(colored(error.msg, "red"))
+        debug.debug_print(error)
+        return 3
     except UnavailableFeatureError as error:
         print(colored(error.msg, "red"))
         debug.debug_print(error)
@@ -99,9 +118,10 @@ def main():
 
     if args.output is not None:
         try:
-            pdf_content = output.to_string()
-            with open(args.output, "wb") as output_file:
-                output_file.write(pdf_content)
+            file_content = output.to_string()
+            opening_mode = get_opening_mode(output_format)
+            with open(args.output, opening_mode) as output_file:
+                output_file.write(file_content)
         except UnavailableFeatureError as error:
             print(colored(error.msg, "red"))
             debug.debug_print(error)
@@ -168,25 +188,35 @@ def get_information(
 
     events_list = get_events(compute_date, timezone)
 
-    return get_dumpers()[output_format](
-        ephemerides=eph,
-        moon_phase=moon_phase,
-        events=events_list,
-        date=compute_date,
-        timezone=timezone,
-        with_colors=colors,
-        show_graph=show_graph,
-    )
+    try:
+        return get_dumpers()[output_format](
+            ephemerides=eph,
+            moon_phase=moon_phase,
+            events=events_list,
+            date=compute_date,
+            timezone=timezone,
+            with_colors=colors,
+            show_graph=show_graph,
+        )
+    except KeyError as error:
+        raise InvalidOutputFormatError(output_format, list(get_dumpers().keys()))
 
 
 def get_dumpers() -> {str: dumper.Dumper}:
     return {
-        "text": dumper.TextDumper,
+        "txt": dumper.TextDumper,
         "json": dumper.JsonDumper,
         "pdf": dumper.PdfDumper,
     }
 
 
+def get_opening_mode(format: str) -> str:
+    if format == "pdf":
+        return "wb"
+
+    return "w"
+
+
 def output_version() -> bool:
     python_version = "%d.%d.%d" % (
         sys.version_info[0],
@@ -254,9 +284,12 @@ def get_args(output_formats: [str]):
         "--format",
         "-f",
         type=str,
-        default=output_formats[0],
+        default=None,
         choices=output_formats,
-        help=_("The format to output the information to"),
+        help=_(
+            "The format to output the information to. If not provided, the output format "
+            "will be inferred from the file extension of the output file."
+        ),
     )
     parser.add_argument(
         "--position",
diff --git a/manpage/kosmorro.1.md b/manpage/kosmorro.1.md
index c27738f..445fca2 100644
--- a/manpage/kosmorro.1.md
+++ b/manpage/kosmorro.1.md
@@ -31,8 +31,8 @@
 `--output=`_OUTPUT_, `-o` _OUTPUT_  
     a file to export the output to; if not given, the standard output is used
 
-`--format=`_FORMAT_, `-f` _FORMAT_  
-    the format under which the information have to be output; one of the following: text, json, pdf
+`--format=`_FORMAT_, `-f` _FORMAT_ (optional)  
+    the format under which the information have to be output; one of the following: text, json, pdf. If no format is provided, the output format will be inferred from the extension of the output file
 
 `--no-graph`  
     present the ephemerides in a table instead of a graph; PDF output format only
@@ -68,7 +68,7 @@ kosmorro --latitude=50.5876 --longitude=3.0624 --date=2022-04-01
 Compute the ephemerides for Lille, France, on April 1st, 2022, and export them in a PDF document:
 
 ```
-kosmorro --latitude=50.5876 --longitude=3.0624 -date=2022-04-01 --format=pdf --output=file.pdf
+kosmorro --latitude=50.5876 --longitude=3.0624 -date=2022-04-01 --output=file.pdf
 ```
 
 ## AUTHOR