diff --git a/autogpt_platform/backend/backend/blocks/mcp/block.py b/autogpt_platform/backend/backend/blocks/mcp/block.py
index f147ffdf5c..339f564f10 100644
--- a/autogpt_platform/backend/backend/blocks/mcp/block.py
+++ b/autogpt_platform/backend/backend/blocks/mcp/block.py
@@ -206,6 +206,45 @@ class MCPToolBlock(Block):
             return output_parts[0]
         return output_parts if output_parts else None
 
+    @staticmethod
+    async def _auto_lookup_credential(
+        user_id: str, server_url: str
+    ) -> "OAuth2Credentials | None":
+        """Auto-lookup stored MCP credential for a server URL.
+
+        This is a fallback for nodes that don't have ``credentials`` explicitly
+        set (e.g. nodes created before the credential field was wired up).
+        """
+        from backend.data.model import Credentials
+        from backend.integrations.creds_manager import IntegrationCredentialsManager
+        from backend.integrations.providers import ProviderName
+
+        try:
+            mgr = IntegrationCredentialsManager()
+            mcp_creds: list[Credentials] = []
+            for prov in (ProviderName.MCP.value, "ProviderName.MCP"):
+                mcp_creds.extend(await mgr.store.get_creds_by_provider(user_id, prov))
+            best: OAuth2Credentials | None = None
+            for cred in mcp_creds:
+                if (
+                    isinstance(cred, OAuth2Credentials)
+                    and cred.metadata.get("mcp_server_url") == server_url
+                ):
+                    if best is None or (
+                        (cred.access_token_expires_at or 0)
+                        > (best.access_token_expires_at or 0)
+                    ):
+                        best = cred
+            if best:
+                best = await mgr.refresh_if_needed(user_id, best)
+                logger.info(
+                    "Auto-resolved MCP credential %s for %s", best.id, server_url
+                )
+            return best
+        except Exception:
+            logger.debug("Auto-lookup MCP credential failed", exc_info=True)
+            return None
+
     async def run(
         self,
         input_data: Input,
@@ -222,6 +261,14 @@ class MCPToolBlock(Block):
             yield "error", "No tool selected. Please select a tool from the dropdown."
             return
 
+        # If no credentials were injected by the executor (e.g. legacy nodes
+        # that don't have the credentials field set), try to auto-lookup
+        # the stored MCP credential for this server URL.
+        if credentials is None:
+            credentials = await self._auto_lookup_credential(
+                user_id, input_data.server_url
+            )
+
         auth_token = (
             credentials.access_token.get_secret_value() if credentials else None
         )
diff --git a/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/CustomNode/useCustomNode.tsx b/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/CustomNode/useCustomNode.tsx
index 6445a339fe..52b491d68e 100644
--- a/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/CustomNode/useCustomNode.tsx
+++ b/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/CustomNode/useCustomNode.tsx
@@ -9,19 +9,25 @@ import { SpecialBlockID } from "@/lib/autogpt-server-api";
  * Build a dynamic input schema for MCP blocks.
  *
  * When a tool has been selected (tool_input_schema is populated), the block
- * renders only the selected tool's input parameters. Credentials are NOT
- * included because authentication is already handled by the MCP dialog's
- * OAuth flow and stored server-side.
+ * renders the selected tool's input parameters *plus* the credentials field
+ * so users can select/change the OAuth credential used for execution.
  *
  * Static fields like server_url, selected_tool, available_tools, and
  * tool_arguments are hidden because they're pre-configured from the dialog.
  */
 function buildMCPInputSchema(
   toolInputSchema: Record<string, any>,
+  blockInputSchema: Record<string, any>,
 ): Record<string, any> {
+  // Extract the credentials field from the block's original input schema
+  const credentialsSchema =
+    blockInputSchema?.properties?.credentials ?? undefined;
+
   return {
     type: "object",
     properties: {
+      // Credentials field first so the dropdown appears at the top
+      ...(credentialsSchema ? { credentials: credentialsSchema } : {}),
       ...(toolInputSchema.properties ?? {}),
     },
     required: [...(toolInputSchema.required ?? [])],
@@ -50,7 +56,10 @@ export const useCustomNode = ({
   const currentInputSchema = isAgent
     ? (data.hardcodedValues.input_schema ?? {})
     : isMCPWithTool
-      ? buildMCPInputSchema(data.hardcodedValues.tool_input_schema)
+      ? buildMCPInputSchema(
+          data.hardcodedValues.tool_input_schema,
+          data.inputSchema,
+        )
       : data.inputSchema;
   const currentOutputSchema = isAgent
     ? (data.hardcodedValues.output_schema ?? {})
diff --git a/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/FormCreator.tsx b/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/FormCreator.tsx
index 839552c867..77b21dda92 100644
--- a/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/FormCreator.tsx
+++ b/autogpt_platform/frontend/src/app/(platform)/build/components/FlowEditor/nodes/FormCreator.tsx
@@ -44,10 +44,13 @@ export const FormCreator: React.FC<FormCreatorProps> = React.memo(
           inputs: formData,
         };
       } else if (isMCPWithTool) {
-        // All form fields are tool arguments (credentials handled by dialog)
+        // Separate credentials from tool arguments — credentials are stored
+        // at the top level of hardcodedValues, not inside tool_arguments.
+        const { credentials, ...toolArgs } = formData;
         updatedValues = {
           ...getHardCodedValues(nodeId),
-          tool_arguments: formData,
+          tool_arguments: toolArgs,
+          ...(credentials?.id ? { credentials } : {}),
         };
       } else {
         updatedValues = formData;
@@ -62,7 +65,13 @@ export const FormCreator: React.FC<FormCreatorProps> = React.memo(
     if (isAgent) {
       initialValues = hardcodedValues.inputs ?? {};
     } else if (isMCPWithTool) {
-      initialValues = hardcodedValues.tool_arguments ?? {};
+      // Merge tool arguments with credentials for the form
+      initialValues = {
+        ...(hardcodedValues.tool_arguments ?? {}),
+        ...(hardcodedValues.credentials?.id
+          ? { credentials: hardcodedValues.credentials }
+          : {}),
+      };
     } else {
       initialValues = hardcodedValues;
     }