diff --git a/.github/workflows/validate-content.yml b/.github/workflows/validate-content.yml
new file mode 100644
index 000000000..0a50cbd98
--- /dev/null
+++ b/.github/workflows/validate-content.yml
@@ -0,0 +1,28 @@
+name: Validate content
+on:
+  push:
+  pull_request:
+    branches: [master, release/*]
+  schedule:
+    - cron: '0 5 * * 1'  # Every Monday 5 AM UTC
+
+jobs:
+  validate-flags:
+    name: Validate flags
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-latest
+          - os: macos-latest
+          - os: windows-latest
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Download source
+        uses: actions/checkout@v4
+      - name: Install Crystal
+        uses: crystal-lang/install-crystal@v1
+        with:
+          crystal: nightly
+      - name: Run test script
+        run: scripts/validate-flags.sh
diff --git a/scripts/validate-flags.sh b/scripts/validate-flags.sh
new file mode 100755
index 000000000..e5aafdfad
--- /dev/null
+++ b/scripts/validate-flags.sh
@@ -0,0 +1,32 @@
+#! /bin/sh
+
+set -eu
+
+CRYSTAL=${CRYSTAL:-crystal}
+CRYSTAL_PATH="$($CRYSTAL env CRYSTAL_PATH)"
+STDLIB_SRC="${CRYSTAL_PATH#*:}" # stdlib source directory is the last entry in CRYSTAL_PATH
+
+filter_missing() {
+  missing=0
+
+  while read -r word; do
+      grep -q "\`$word\`" docs/syntax_and_semantics/compile_time_flags.md || {
+        [ ${missing} -eq 0 ] && echo "# Missing ${1} flags:"
+        echo "$word"
+        missing=1
+      }
+    done
+  return ${missing}
+}
+
+status=0
+find "${STDLIB_SRC}" -name '*.cr' -type f -not -path "${STDLIB_SRC}/compiler/**" -print0 \
+  | xargs -0 "${CRYSTAL}" tool flags \
+  | filter_missing "stdlib" || status=1
+
+{
+  ${CRYSTAL} tool flags "${STDLIB_SRC}/compiler"
+  grep --no-file -o -R -P '(?<=has_flag\?[( ]")[^"]+' "${STDLIB_SRC}/compiler"
+} | sort -u | filter_missing "compiler" || status=1
+
+exit ${status}