diff --git a/.github/workflows/check-qldoc.yml b/.github/workflows/check-qldoc.yml
new file mode 100644
index 00000000000..146c7d77b7c
--- /dev/null
+++ b/.github/workflows/check-qldoc.yml
@@ -0,0 +1,50 @@
+name: "Check QLdoc"
+
+on:
+  pull_request:
+    paths:
+      - "*/ql/lib/**"
+      - .github/workflows/check-qldoc.yml
+    branches:
+      - main
+      - "rc/*"
+
+jobs:
+  qldoc:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Install CodeQL
+        run: |
+          gh extension install github/gh-codeql
+          gh codeql set-channel nightly
+          gh codeql version
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
+
+      - name: Check QLdoc
+        shell: bash
+        run: |
+          EXIT_CODE=0
+          changed_lib_packs="$(git diff --name-only --diff-filter=ACMRT HEAD^ HEAD | { grep -o '^[a-z]*/ql/lib' || true; } | sort -u)"
+          for pack_dir in ${changed_lib_packs}; do
+            lang="${pack_dir%/ql/lib}"
+            gh codeql generate library-doc-coverage --output="${{ runner.temp }}/${lang}-current.txt" --dir="${pack_dir}"
+          done
+          git checkout HEAD^
+          for pack_dir in ${changed_lib_packs}; do
+            lang="${pack_dir%/ql/lib}"
+            gh codeql generate library-doc-coverage --output="${{ runner.temp }}/${lang}-baseline.txt" --dir="${pack_dir}"
+            awk -F, '{gsub(/"/,""); if ($4==0 && $6=="public") print "\""$3"\"" }' "${{ runner.temp }}/${lang}-current.txt" | sort -u > "${{ runner.temp }}/current-undocumented.txt"
+            awk -F, '{gsub(/"/,""); if ($4==0 && $6=="public") print "\""$3"\"" }' "${{ runner.temp }}/${lang}-baseline.txt" | sort -u > "${{ runner.temp }}/baseline-undocumented.txt"
+            UNDOCUMENTED="$(grep -f <(comm -13 "${{ runner.temp }}/baseline-undocumented.txt" "${{ runner.temp }}/current-undocumented.txt") "${{ runner.temp }}/${lang}-current.txt" || true)"
+            if [ -n "$UNDOCUMENTED" ]; then
+              echo "$UNDOCUMENTED" | awk -F, '{gsub(/"/,""); print "::warning file='"${pack_dir}"'/"$1",line="$2"::Missing QLdoc for "$5, $3 }'
+              EXIT_CODE=1
+            fi
+          done
+          exit "${EXIT_CODE}"