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fix(mcp): rebind page-registered WebMCP tools when the tab or frame changes #42821

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fix(mcp): rebind page-registered WebMCP tools when the tab or frame changes #42821

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0b33e74
fix(mcp): rebind page-registered WebMCP tools when the tab or frame c…
Abnoz01 Sep 20, 2026
8dab074
fix(mcp): read WebMCP tools from the current tab instead of caching them
Abnoz01 Sep 22, 2026
9b4ac8a
Merge remote-tracking branch 'origin/main' into fix-42816
Abnoz01 Sep 22, 2026
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8 changes: 3 additions & 5 deletions packages/playwright-core/src/tools/backend/context.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -119,7 +119,6 @@ export class Context {
private _recordedActions: string[] | undefined;
private _disposables: Disposable[] = [];

private _webmcpTools: WebMCPToolDefinition[] = [];
private _webmcpToolsSignature = '';

private _runningToolName: string | undefined;
Expand Down Expand Up @@ -328,16 +327,15 @@ export class Context {
}

currentWebMCPTools(): WebMCPToolDefinition[] {
return this._webmcpTools;
// Handlers are bound to a tab and frame, always take the fresh ones.
return this._currentTab?.webmcpTools()?.tools.map(tool => tool.mcpTool) ?? [];
}

maybeNotifyWebMCPToolsChanged() {
const tools = this._currentTab?.webmcpTools()?.tools.map(tool => tool.mcpTool) ?? [];
const signature = JSON.stringify(tools.map(tool => tool.schema));
const signature = JSON.stringify(this.currentWebMCPTools().map(tool => tool.schema));
if (signature === this._webmcpToolsSignature)
return;
this._webmcpToolsSignature = signature;
this._webmcpTools = tools;
this.options.onWebMCPToolsChanged?.();
}

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23 changes: 23 additions & 0 deletions tests/mcp/webmcp-dynamic.spec.ts
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Expand Up @@ -186,6 +186,29 @@ test('only the current tab contributes tools, switching tabs swaps them', async
expect(await names()).toEqual(['webmcp_add']);
});

test('a tool registered in an iframe can be called after the page is reloaded', async ({ startClient, server, mcpBrowser }) => {
test.skip(mcpBrowser === 'firefox', 'Firefox does not list tools registered in iframes');
server.setRoute('/frame', (req, res) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(`<title>frame</title>${registerScript(kAdd)}`);
});
server.setRoute('/', (req, res) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(`<title>top</title><iframe src="/frame"></iframe>`);
});

const { client } = await startClient({ config: webmcpConfig(mcpBrowser) });
await client.callTool({ name: 'browser_navigate', arguments: { url: server.PREFIX } });
expect(await client.callTool({ name: 'webmcp_add', arguments: { a: 1, b: 2 } })).toHaveResponse({
result: expect.stringContaining('"text": "3"'),
});

await client.callTool({ name: 'browser_navigate', arguments: { url: server.PREFIX } });
expect(await client.callTool({ name: 'webmcp_add', arguments: { a: 2, b: 3 } })).toHaveResponse({
result: expect.stringContaining('"text": "5"'),
});
});

test('--no-webmcp opts out of page tools entirely', async ({ startClient, server, mcpBrowser }) => {
server.setRoute('/', (req, res) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
Expand Down
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