cache cdp session

playwriter/src/mcp.ts

@@ -88,6 +88,9 @@ const MAX_LOGS_PER_PAGE = 5000
 // Store last accessibility snapshot per page for diff feature
 const lastSnapshots: WeakMap<Page, string> = new WeakMap()
 
+// Cache CDP sessions per page
+const cdpSessionCache: WeakMap<Page, CDPSession> = new WeakMap()
+
 const RELAY_PORT = 19988
 const LOG_FILE_PATH = process.env.PLAYWRITER_LOG_PATH || path.join(os.tmpdir(), 'playwriter-relay-server.log')
 const NO_TABS_ERROR = `No browser tabs are connected. Please install and enable the Playwriter extension on at least one tab: https://chromewebstore.google.com/detail/playwriter-mcp/jfeammnjpkecdekppnclgkkffahnhfhe`
@@ -536,8 +539,14 @@ server.tool(
       }
 
       const getCDPSession = async (options: { page: Page }) => {
+        const cached = cdpSessionCache.get(options.page)
+        if (cached) {
+          return cached
+        }
         const wsUrl = getCdpUrl({ port: RELAY_PORT })
-        return getCDPSessionForPage({ page: options.page, wsUrl })
+        const session = await getCDPSessionForPage({ page: options.page, wsUrl })
+        cdpSessionCache.set(options.page, session)
+        return session
       }
 
       let vmContextObj: VMContextWithGlobals = {

playwriter/src/prompt.md

@@ -89,12 +89,18 @@ you have access to some functions in addition to playwright methods:
     - `minWait`: (optional) minimum wait before checking in ms (default: 500)
     - Returns: `{ success, readyState, pendingRequests, waitTimeMs, timedOut }`
     - Filters out: ad networks (doubleclick, googlesyndication), analytics (google-analytics, mixpanel, segment), social (facebook.net, twitter), support widgets (intercom, zendesk), and slow fonts/images
-- `getCDPSession({ page })`: creates a CDP session to send raw Chrome DevTools Protocol commands. Use this instead of `page.context().newCDPSession()` which does not work through the playwriter relay.
+- `getCDPSession({ page })`: creates a CDP session to send raw Chrome DevTools Protocol commands. Use this instead of `page.context().newCDPSession()` which does not work through the playwriter relay. Sessions are cached per page.
     - `page`: the page object to create the session for
-    - Returns: `{ send(method, params?), on(event, callback), off(event, callback), detach() }`
+    - Returns: `{ send(method, params?), on(event, callback), off(event, callback) }`
-    - Example: `const cdp = await getCDPSession({ page }); const metrics = await cdp.send('Page.getLayoutMetrics'); cdp.detach();`
+    - Example: `const cdp = await getCDPSession({ page }); const metrics = await cdp.send('Page.getLayoutMetrics');`
-
+    - Example listening for events:
-To bring a tab to front and focus it, use the standard Playwright method `await page.bringToFront()`
+      ```js
+      const cdp = await getCDPSession({ page });
+      await cdp.send('Debugger.enable');
+      const pausedEvent = await new Promise((resolve) => { cdp.on('Debugger.paused', resolve); });
+      console.log('Paused at:', pausedEvent.callFrames[0].location);
+      await cdp.send('Debugger.resume');
+      ```
 
 example: