diff --git a/web/src/pages/flow/constant.tsx b/web/src/pages/flow/constant.tsx
index 4da80de48c..60f1887b1f 100644
--- a/web/src/pages/flow/constant.tsx
+++ b/web/src/pages/flow/constant.tsx
@@ -254,6 +254,9 @@ export const RestrictedUpstreamMap = {
     Operator.Categorize,
     Operator.Relevant,
   ],
+  [Operator.KeywordExtract]: [Operator.Begin],
+  [Operator.Baidu]: [Operator.Begin],
+  [Operator.DuckDuckGo]: [Operator.Begin],
 };
 
 export const NodeMap = {
diff --git a/web/src/pages/flow/hooks.ts b/web/src/pages/flow/hooks.ts
index 3d3b103652..e052fb773e 100644
--- a/web/src/pages/flow/hooks.ts
+++ b/web/src/pages/flow/hooks.ts
@@ -297,12 +297,16 @@ export const useValidateConnection = () => {
   // restricted lines cannot be connected successfully.
   const isValidConnection = useCallback(
     (connection: Connection) => {
+      // node cannot connect to itself
+      const isSelfConnected = connection.target === connection.source;
+
       // limit the connection between two nodes to only one connection line in one direction
       const hasLine = edges.some(
         (x) => x.source === connection.source && x.target === connection.target,
       );
 
       const ret =
+        !isSelfConnected &&
         !hasLine &&
         RestrictedUpstreamMap[
           getOperatorTypeFromId(connection.source) as Operator