diff --git a/CHANGELOG.md b/CHANGELOG.md
index 61f1b05..afd3606 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- *Action required:* Move existing behaviour under "parse" subcommand.
+  Invocations of `mypy-json-report` should now be replaced with `mypy-json-report parse`.
 - Use GA version of Python 3.11 in test matrix.
 
 ## v0.1.3 [2022-09-07]
diff --git a/README.md b/README.md
index 502abca..87283bf 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ Pipe the output of mypy through the `mypy-json-report` CLI app.
 Store the output to a file, and commit it to your git repo.
 
 ```
-mypy . --strict | mypy-json-report > known-mypy-errors.json
+mypy . --strict | mypy-json-report parse > known-mypy-errors.json
 git add known-mypy-errors.json
 git commit -m "Add mypy errors lockfile"
 ```
@@ -80,7 +80,7 @@ jobs:
 
       - name: Run mypy
         run: |
-          mypy . --strict | mypy-json-report > known-mypy-errors.json
+          mypy . --strict | mypy-json-report parse > known-mypy-errors.json
 
       - name: Check for mypy changes
         run: |
diff --git a/mypy_json_report.py b/mypy_json_report.py
index a00ede9..f7db976 100644
--- a/mypy_json_report.py
+++ b/mypy_json_report.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
+import enum
 import json
 import sys
 from collections import Counter, defaultdict
@@ -19,16 +21,50 @@
 from typing import Counter as CounterType, Dict, Iterator
 
 
+class ErrorCodes(enum.IntEnum):
+    DEPRECATED = 1
+
+
 def main() -> None:
-    report_errors()
+    """
+    The primary entrypoint of the program.
+
+    Parses the CLI flags, and delegates to other functions as appropriate.
+    For details of how to invoke the program, call it with `--help`.
+    """
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers(title="subcommand")
+
+    parser.set_defaults(func=_no_command)
+
+    parse_parser = subparsers.add_parser(
+        "parse", help="Transform Mypy output into JSON."
+    )
 
+    parse_parser.set_defaults(func=_parse_command)
 
-def report_errors() -> None:
+    args = sys.argv[1:]
+    parsed = parser.parse_args(args)
+    parsed.func(parsed)
+
+
+def _parse_command(args: object) -> None:
+    """Handle the `parse` command."""
     errors = parse_errors_report(sys.stdin)
     error_json = json.dumps(errors, sort_keys=True, indent=2)
     print(error_json)
 
 
+def _no_command(args: object) -> None:
+    """
+    Handle the lack of an explicit command.
+
+    This will be hit when the program is called without arguments.
+    """
+    print("A subcommand is required. Pass --help for usage info.")
+    sys.exit(ErrorCodes.DEPRECATED)
+
+
 @dataclass(frozen=True)
 class MypyError:
     filename: str
diff --git a/tox.ini b/tox.ini
index d211354..9ab2b06 100644
--- a/tox.ini
+++ b/tox.ini
@@ -39,5 +39,5 @@ allowlist_externals =
 commands_pre =
     poetry install
 commands =
-    poetry run bash -c "mypy . --strict | mypy-json-report > known-mypy-errors.json"
+    poetry run bash -c "mypy . --strict | mypy-json-report parse > known-mypy-errors.json"
     git diff --exit-code known-mypy-errors.json