diff --git a/openapi/diff-optic/action.yaml b/openapi/diff-optic/action.yaml
new file mode 100644
index 0000000..7bb3e24
--- /dev/null
+++ b/openapi/diff-optic/action.yaml
@@ -0,0 +1,21 @@
+name: Compare OpenAPI specs
+inputs:
+  openapi-uri-original:
+    description: URI (file or URL) to the original OpenAPI spec ("before")
+    required: true
+  openapi-uri-updated:
+    description: URI (file or URL) to the updated OpenAPI spec ("after")
+    required: true
+  optic-yaml-path:
+    description: (Optional) Path to an Optic YAML file, for customizing the Optic diff ruleset
+    required: false
+
+runs:
+  using: composite
+  steps:
+    - shell: bash
+      run: ${{ github.action_path }}/run.sh
+      env: 
+        OPENAPI_URI_ORIGINAL: ${{ inputs.openapi-uri-original }}
+        OPENAPI_URI_UPDATED: ${{ inputs.openapi-uri-updated }}
+        OPTIC_YAML_PATH: ${{ inputs.optic-yaml-path }}
diff --git a/openapi/diff-optic/run.sh b/openapi/diff-optic/run.sh
new file mode 100755
index 0000000..0c798df
--- /dev/null
+++ b/openapi/diff-optic/run.sh
@@ -0,0 +1,42 @@
+#!/bin/bash
+set -xe
+
+echo "🔍 Checking for API breaking changes..."
+
+npm install -g @useoptic/optic
+
+OPTIC_ARGS=(diff "${OPENAPI_URI_ORIGINAL}" "${OPENAPI_URI_UPDATED}")
+
+if [ -n "${OPTIC_YAML_PATH}" ]; then
+    OPTIC_ARGS+=(--standard "${OPTIC_YAML_PATH}")
+fi
+
+if ! optic "${OPTIC_ARGS[@]}" --severity error 2>/dev/null; then
+    echo "❌ Breaking API changes detected!"
+    BREAKING_CHANGES=true
+else
+    echo "✅ No breaking API changes"
+fi
+
+echo ""
+echo "=================================================================="
+
+if [ "$BREAKING_CHANGES" = true ]; then
+    echo "❌ API BREAKING CHANGES DETECTED!"
+    echo ""
+    echo "🚨 This PR contains potentially breaking changes:"
+    echo "   • .NET assembly API changes, or"
+    echo "   • HTTP endpoint route changes, or"
+    echo "   • Removed HTTP endpoints"
+    echo ""
+    echo "If these changes are intentional:"
+    echo "1. 📈 Update version numbers appropriately"
+    echo "2. 📝 Document breaking changes in your PR description"
+    echo "3. 🤔 Consider the impact on existing API consumers"
+    echo "4. 📧 Notify teams that depend on these APIs"
+    echo ""
+    exit 1
+else
+    echo "✅ API COMPATIBILITY CHECK PASSED!"
+    echo "No breaking changes detected in HTTP endpoints."
+fi