fix: Handle errors during tool calls and check if a dialog is open

This change also adds a check for existence of open dialogs before trying to detect open devtools

ran prettier

add try catch block in index.ts to handle dialog

add test

add test

ran prettier

ran prettier

update test to use snapshot assertion

Update handling of errors from tool execution

mark isError as true

Author: samiyac

src/McpResponse.ts

@@ -203,6 +203,7 @@ export class McpResponse implements Response {
   #args: ParsedArguments;
   #page?: McpPage;
   #redactNetworkHeaders = true;
+  #error?: Error;
 
   constructor(args: ParsedArguments) {
     this.#args = args;
@@ -307,6 +308,10 @@ export class McpResponse implements Response {
     };
   }
 
+  setError(error: Error): void {
+    this.#error = error;
+  }
+
   attachNetworkRequest(
     reqId: number,
     options?: {requestFilePath?: string; responseFilePath?: string},
@@ -375,6 +380,10 @@ export class McpResponse implements Response {
     return this.#consoleDataOptions?.types;
   }
 
+  get error(): Error | undefined {
+    return this.#error;
+  }
+
   appendResponseLine(value: string): void {
     this.#textResponseLines.push(value);
   }
@@ -662,6 +671,7 @@ export class McpResponse implements Response {
       lighthouseResult: this.#attachedLighthouseResult,
       inPageTools,
       webmcpTools,
+      errorMessage: this.#error?.message,
     });
   }
 
@@ -680,6 +690,7 @@ export class McpResponse implements Response {
       lighthouseResult?: LighthouseData;
       inPageTools?: ToolGroup<ToolDefinition>;
       webmcpTools?: WebMCPTool[];
+      errorMessage?: string;
     },
   ): {content: Array<TextContent | ImageContent>; structuredContent: object} {
     const structuredContent: {
@@ -718,6 +729,7 @@ export class McpResponse implements Response {
       heapSnapshotNodes?: readonly object[];
       extensionServiceWorkers?: object[];
       extensionPages?: object[];
+      errorMessage?: string;
     } = {};
 
     const response = [];
@@ -1080,6 +1092,11 @@ Call ${handleDialog.name} to handle it before continuing.`);
       }
     }
 
+    if (data.errorMessage) {
+      response.push(`Error: ${data.errorMessage}`);
+      structuredContent.errorMessage = data.errorMessage;
+    }
+
     const text: TextContent = {
       type: 'text',
       text: response.join('\n'),

src/WaitForHelper.ts

@@ -128,8 +128,10 @@ export class WaitForHelper {
     action: () => Promise<unknown>,
     options?: {timeout?: number; handleDialog?: 'accept' | 'dismiss' | string},
   ): Promise<void> {
+    let dialogOpened = false;
     if (options?.handleDialog) {
       const dialogHandler = (dialog: Pick<Dialog, 'accept' | 'dismiss'>) => {
+        dialogOpened = true;
         if (options.handleDialog === 'dismiss') {
           void dialog.dismiss();
         } else if (options.handleDialog === 'accept') {
@@ -167,6 +169,10 @@ export class WaitForHelper {
     try {
       await navigationFinished;
 
+      if (dialogOpened) {
+        return;
+      }
+
       // Wait for stable dom after navigation so we execute in
       // the correct context
       await this.waitForStableDom();

src/index.ts

@@ -232,31 +232,35 @@ export async function createMcpServer(
             : new McpResponse(serverArgs);
 
           response.setRedactNetworkHeaders(serverArgs.redactNetworkHeaders);
-          if ('pageScoped' in tool && tool.pageScoped) {
-            const page =
-              serverArgs.experimentalPageIdRouting &&
-              params.pageId &&
-              !serverArgs.slim
-                ? context.getPageById(params.pageId)
-                : context.getSelectedMcpPage();
-            response.setPage(page);
-            await tool.handler(
-              {
-                params,
-                page,
-              },
-              response,
-              context,
-            );
-          } else {
-            await tool.handler(
-              // @ts-expect-error types do not match.
-              {
-                params,
-              },
-              response,
-              context,
-            );
+          try {
+            if ('pageScoped' in tool && tool.pageScoped) {
+              const page =
+                serverArgs.experimentalPageIdRouting &&
+                params.pageId &&
+                !serverArgs.slim
+                  ? context.getPageById(params.pageId)
+                  : context.getSelectedMcpPage();
+              response.setPage(page);
+              await tool.handler(
+                {
+                  params,
+                  page,
+                },
+                response,
+                context,
+              );
+            } else {
+              await tool.handler(
+                // @ts-expect-error types do not match.
+                {
+                  params,
+                },
+                response,
+                context,
+              );
+            }
+          } catch (err) {
+            response.setError(err);
           }
           const {content, structuredContent} = await response.handle(
             tool.name,
@@ -267,6 +271,9 @@ export async function createMcpServer(
           } = {
             content,
           };
+          if (response.error) {
+            result.isError = true;
+          }
           success = true;
           if (serverArgs.experimentalStructuredContent) {
             result.structuredContent = structuredContent as Record<

tests/index.test.js.snapshot

@@ -5,3 +5,7 @@ exports[`e2e > calls a tool 1`] = `
 exports[`e2e > calls a tool multiple times 1`] = `
 [{"type":"text","text":"## Pages\\n1: about:blank [selected]"}]
 `;
+
+exports[`e2e > returns blocked message when dialog is opened during tool execution 1`] = `
+{"content":[{"type":"text","text":"# Open dialog\\nalert: test dialog.\\nCall handle_dialog to handle it before continuing.\\nError: Failed to interact with the element with uid 1_1. The element did not become interactive within the configured timeout."}],"isError":true}
+`;

tests/index.test.ts

@@ -245,6 +245,37 @@ describe('e2e', () => {
       },
     );
   });
+
+  it('returns blocked message when dialog is opened during tool execution', async t => {
+    await withClient(async client => {
+      // Navigate to a page with a button that triggers a dialog on click
+      await client.callTool({
+        name: 'new_page',
+        arguments: {
+          url: `data:text/html,<button id="test" onclick="alert('test dialog')">Click me</button>`,
+        },
+      });
+
+      const snapshotResult = await client.callTool({
+        name: 'take_snapshot',
+        arguments: {},
+      });
+
+      const snapshotText = (snapshotResult.content as TextContent[])[0].text;
+      const match = snapshotText.match(/uid=(\d+_\d+)\s+button "Click me"/);
+      const uid = match ? match[1] : '1_1';
+
+      // Trigger the dialog
+      const result = await client.callTool({
+        name: 'click',
+        arguments: {
+          uid,
+        },
+      });
+
+      t.assert.snapshot?.(JSON.stringify(result));
+    });
+  });
 });
 
 async function getToolsWithFilteredCategories(