diff --git a/src/presentation/nodeWatcher/NodeWatcher.port.ts b/src/presentation/nodeWatcher/NodeWatcher.port.ts
new file mode 100644
index 0000000..83372b6
--- /dev/null
+++ b/src/presentation/nodeWatcher/NodeWatcher.port.ts
@@ -0,0 +1,23 @@
+import { NodeWatcherHandler } from "./NodeWatcherHandler";
+
+export interface NodeWatcherPort {
+  /**
+   * Start watching mutations to nodes.
+   */
+  start(): void;
+
+  /**
+   * Pause watching mutations to nodes.
+   */
+  pause(): void;
+
+  /**
+   * Add a handler to watch certain mutations.
+   */
+  setHandler(key: string, handler: NodeWatcherHandler): void;
+
+  /**
+   * Remove a handler by key.
+   */
+  removeHandler(key: string): boolean;
+}