diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..78eb3ee
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,27 @@
+[run]
+include = appengine/monorail/*
+omit =
+    # Add monorail's third-party packages and worst offenders
+    ./appengine/monorail/third_party/*
+    ./appengine/monorail/lib/*
+    ./appengine/monorail/testing/*
+    ./appengine/monorail/**/test/*
+[report]
+exclude_lines =
+    # Have to re-enable the standard pragma
+    pragma: no cover
+
+    # Don't complain about missing debug-only code:
+    def __repr__
+    if self\.debug
+
+    # Don't complain if tests don't hit defensive assertion code:
+    raise AssertionError
+    raise NotImplementedError
+
+    # Don't complain if non-runnable code isn't run:
+    if 0:
+    if __name__ == ['"]__main__['"]:
+
+[expect_tests]
+expected_coverage_min = 84