diff --git a/packages/web-performance/src/index.ts b/packages/web-performance/src/index.ts
index 99b4d1a9..8ee0d2b7 100644
--- a/packages/web-performance/src/index.ts
+++ b/packages/web-performance/src/index.ts
@@ -50,6 +50,7 @@ class WebVitals implements IWebVitals {
     this.immediately = immediately
 
     const sessionId = generateUniqueID()
+    window.__monitor_sessionId__ = sessionId
     reporter = createReporter(sessionId, appId, version, reportCallback)
     metricsStore = new MetricsStore()
 
diff --git a/packages/web-performance/src/types/index.ts b/packages/web-performance/src/types/index.ts
index fc07b4dd..88a18b6f 100644
--- a/packages/web-performance/src/types/index.ts
+++ b/packages/web-performance/src/types/index.ts
@@ -131,5 +131,6 @@ declare global {
     // Build flags:
     __monitor_xhr__: boolean
     __monitor_fetch__: boolean
+    __monitor_sessionId__: string
   }
 }