diff --git a/.github/workflows/test-action-pr501-r2.yml b/.github/workflows/test-action-pr501-r2.yml
new file mode 100644
index 0000000..f386e5a
--- /dev/null
+++ b/.github/workflows/test-action-pr501-r2.yml
@@ -0,0 +1,161 @@
+# Temporary: end-to-end check of cpp-linter/cpp-linter-action#501
+# (cpp-linter 1.14.1 -> 1.15.1, clang-tools 1.3.0 -> 2.0.0). Remove after the test.
+name: test action#501 (1.15.1 + clang-tools 2.0.0)
+
+on:
+  # round 2: pull_request only (the push matrix already ran on 2a0076d)
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  candidate:
+    name: "candidate ${{ matrix.os }}"
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, ubuntu-24.04-arm, macos-latest, windows-latest, windows-11-arm]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - name: Generate compilation database
+        run: cmake -Bbuild src
+      - name: Run cpp-linter-action (cpp-linter 1.15.1, clang-tools 2.0.0)
+        uses: cpp-linter/cpp-linter-action@fc065f1b186a95c585df750b8007b0fe2f487800
+        id: linter
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          style: file
+          version: '20'
+          ignore: build
+          database: build
+          verbosity: debug
+          extra-args: -std=c++14 -Wall
+          files-changed-only: ${{ github.event_name == 'pull_request' }}
+          step-summary: true
+          file-annotations: true
+          thread-comments: ${{ matrix.os == 'ubuntu-latest' && 'update' || 'false' }}
+          tidy-review: ${{ matrix.os == 'ubuntu-latest' && github.event_name == 'pull_request' }}
+          format-review: ${{ matrix.os == 'ubuntu-latest' && github.event_name == 'pull_request' }}
+      - name: Outputs
+        shell: bash
+        run: |
+          echo "total: ${{ steps.linter.outputs.checks-failed }}"
+          echo "clang-format: ${{ steps.linter.outputs.clang-format-checks-failed }}"
+          echo "clang-tidy: ${{ steps.linter.outputs.clang-tidy-checks-failed }}"
+          command -v clang-tidy-20 clang-format-20 || true
+          ls -la ~/.local/share/clang-tools 2>/dev/null || true
+
+  baseline:
+    name: "main ${{ matrix.os }}"
+    if: github.event_name == 'push'
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, ubuntu-24.04-arm, macos-latest, windows-latest, windows-11-arm]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - name: Generate compilation database
+        run: cmake -Bbuild src
+      - name: Run cpp-linter-action at main (cpp-linter 1.14.1, clang-tools 1.3.0)
+        uses: cpp-linter/cpp-linter-action@f16b974d2b12ac48190748a973e67d50603e9826
+        id: linter
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          style: file
+          version: '20'
+          ignore: build
+          database: build
+          verbosity: debug
+          extra-args: -std=c++14 -Wall
+          files-changed-only: false
+          step-summary: true
+          file-annotations: false
+          thread-comments: false
+      - name: Outputs
+        shell: bash
+        run: |
+          echo "total: ${{ steps.linter.outputs.checks-failed }}"
+          echo "clang-format: ${{ steps.linter.outputs.clang-format-checks-failed }}"
+          echo "clang-tidy: ${{ steps.linter.outputs.clang-tidy-checks-failed }}"
+
+  versions:
+    # every supported clang version on each OS: clang-tools 2.0.0 installs
+    # the static binaries (Windows, and wherever the system has no such version)
+    name: "${{ matrix.ref == 'fc065f1b186a95c585df750b8007b0fe2f487800' && 'candidate' || 'main' }} ${{ matrix.os }} clang ${{ matrix.version }}"
+    if: github.event_name == 'push'
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        version: ['12', '13', '14', '15', '16', '17', '18', '19', '20', '21', '22', '23']
+        ref:
+          - fc065f1b186a95c585df750b8007b0fe2f487800
+          - f16b974d2b12ac48190748a973e67d50603e9826
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - name: Generate compilation database
+        run: cmake -Bbuild src
+      - name: Check out the action
+        uses: actions/checkout@v7
+        with:
+          repository: cpp-linter/cpp-linter-action
+          ref: ${{ matrix.ref }}
+          path: action-under-test
+          persist-credentials: false
+      - name: Run cpp-linter-action
+        uses: ./action-under-test
+        id: linter
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          style: file
+          version: ${{ matrix.version }}
+          ignore: build|action-under-test
+          database: build
+          extra-args: -std=c++14 -Wall
+          files-changed-only: false
+          step-summary: false
+          file-annotations: false
+          thread-comments: false
+      - name: Outputs
+        shell: bash
+        run: |
+          echo "result: total=${{ steps.linter.outputs.checks-failed }} format=${{ steps.linter.outputs.clang-format-checks-failed }} tidy=${{ steps.linter.outputs.clang-tidy-checks-failed }}"
+
+  auto-fix:
+    name: "candidate auto-fix"
+    if: always() && github.event_name == 'pull_request'
+    # run after the review job so the pushed fix does not change the PR diff mid-review
+    needs: candidate
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          ref: ${{ github.head_ref }}
+      - name: Run cpp-linter-action with auto-fix
+        uses: cpp-linter/cpp-linter-action@fc065f1b186a95c585df750b8007b0fe2f487800
+        id: linter
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          style: file
+          version: '20'
+          tidy-checks: '-*'
+          files-changed-only: true
+          thread-comments: false
+          step-summary: true
+          auto-fix: true
diff --git a/src/demo.cpp b/src/demo.cpp
index 0c1db60..4ca436b 100644
--- a/src/demo.cpp
+++ b/src/demo.cpp
@@ -1,7 +1,7 @@
 /** This is a very ugly test code (doomed to fail linting) */
 #include "demo.hpp"
-#include <cstdio>
 #include <cstddef>
+#include <cstdio>
 
 // using size_t from cstddef
 size_t dummyFunc(size_t i) { return i; }
@@ -15,3 +15,18 @@ int main()
 
     return 0;
 }
+
+// added to test cpp-linter-action#501 (temporary)
+int addNumbers(int a, int b)
+{
+    int* unused = NULL;
+    if (a > b)
+        return a + b;
+    return b + a;
+}
+
+// second round (temporary)
+int subtract(int x, int y) { return x - y; }
+
+// round 2: badly formatted on purpose (temporary)
+int multiply(int x, int y) { return x * y; }