diff --git a/ci/check_and_fix_format.sh b/ci/check_and_fix_format.sh
index 7ae4a7ca2d0b..7d5fe0a54d18 100755
--- a/ci/check_and_fix_format.sh
+++ b/ci/check_and_fix_format.sh
@@ -4,6 +4,12 @@ set -e
 
 DIFF_OUTPUT="${DIFF_OUTPUT:-/build/fix_format.diff}"
 
+# We set this for two reasons. First, we want to ensure belt-and-braces that we check these formats
+# in CI in case the skip-on-file-change heuristics in proto_format.sh etc. are buggy. Second, this
+# prevents AZP cache weirdness.
+export FORCE_PROTO_FORMAT=yes
+export FORCE_PYTHON_FORMAT=yes
+
 function fix {
   set +e
   ci/do_ci.sh fix_format
diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 3194460a27c3..5495afaceded 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -303,12 +303,10 @@ elif [[ "$CI_TARGET" == "bazel.fuzzit" ]]; then
 elif [[ "$CI_TARGET" == "fix_format" ]]; then
   # proto_format.sh needs to build protobuf.
   setup_clang_toolchain
-  echo "protoxform_test..."
-  ./tools/protoxform/protoxform_test.sh
   echo "fix_format..."
   ./tools/code_format/check_format.py fix
   ./tools/code_format/format_python_tools.sh fix
-  ./tools/proto_format/proto_format.sh fix
+  ./tools/proto_format/proto_format.sh fix --test
   exit 0
 elif [[ "$CI_TARGET" == "check_format" ]]; then
   # proto_format.sh needs to build protobuf.
diff --git a/tools/code_format/format_python_tools.sh b/tools/code_format/format_python_tools.sh
index 56587489a73a..ac755e3dff52 100755
--- a/tools/code_format/format_python_tools.sh
+++ b/tools/code_format/format_python_tools.sh
@@ -1,5 +1,9 @@
 #!/bin/bash
 
+"$(dirname "$0")"/../git/modified_since_last_github_commit.sh ./ py || \
+  [[ "${FORCE_PYTHON_FORMAT}" == "yes" ]] || \
+  { echo "Skipping format_python_tools.sh due to no Python changes"; exit 0; }
+
 . tools/shell_utils.sh
 
 set -e
diff --git a/tools/git/last_github_commit.sh b/tools/git/last_github_commit.sh
new file mode 100755
index 000000000000..9746d259ac3b
--- /dev/null
+++ b/tools/git/last_github_commit.sh
@@ -0,0 +1,8 @@
+#!/bin/bash
+
+# Looking back from HEAD, find the first commit that was merged onto master by GitHub. This is
+# likely the last non-local change on a given branch. There may be some exceptions for this
+# heuristic, e.g. when patches are manually merged for security fixes on master, but this is very
+# rare.
+
+git rev-list --no-merges --committer="GitHub <noreply@github.com>" --max-count=1 HEAD
diff --git a/tools/git/modified_since_last_github_commit.sh b/tools/git/modified_since_last_github_commit.sh
new file mode 100755
index 000000000000..bbb9d388a239
--- /dev/null
+++ b/tools/git/modified_since_last_github_commit.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+declare -r BASE="$(dirname "$0")"
+declare -r TARGET_PATH=$1
+declare -r EXTENSION=$2
+
+git diff --name-only $("${BASE}"/last_github_commit.sh)..HEAD | grep "\.${EXTENSION}$"
diff --git a/tools/proto_format/proto_format.sh b/tools/proto_format/proto_format.sh
index 9b2fe06b92a0..c899c284fb4b 100755
--- a/tools/proto_format/proto_format.sh
+++ b/tools/proto_format/proto_format.sh
@@ -6,6 +6,17 @@ set -e
 
 [[ "$1" == "check" || "$1" == "fix" ]] || (echo "Usage: $0 <check|fix>"; exit 1)
 
+# Developers working on protoxform and other proto format tooling changes will need to override the
+# following check by setting FORCE_PROTO_FORMAT=yes in the environment.
+./tools/git/modified_since_last_github_commit.sh ./api/envoy proto || \
+  [[ "${FORCE_PROTO_FORMAT}" == "yes" ]] || \
+  { echo "Skipping proto_format.sh due to no API change"; exit 0; }
+
+if [[ "$2" == "--test" ]]
+then
+  ./tools/protoxform/protoxform_test.sh
+fi
+
 # Clean up any stale files in the API tree output. Bazel remembers valid cached
 # files still.
 # rm -rf bazel-bin/external/envoy_api