How to Test and Optimise Back/Forward Cache (bfcache) Using Google Chrome DevTools

The Back/Forward Cache (commonly referred to as bfcache) is one of the most impactful browser optimisations for modern web performance. When a user navigates away from a webpage, instead of terminating the JavaScript execution environment and tearing down the DOM, the browser freezes the entire memory snapshot and preserves it in an in-memory cache. If the user subsequently clicks the Back or Forward navigation buttons, the browser restores the page instantaneously without refetching assets or re-executing initial rendering lifecycles. However, minor code patterns—such as open WebSocket connections, active unload event listeners, or unsupported Permissions-Policy directives—silently disqualify pages from bfcache eligibility. Google Chrome DevTools provides a dedicated diagnostic suite to test, evaluate, and resolve these blocking reasons directly.

Locating the Back/Forward Cache Panel in Chrome DevTools

The bfcache diagnostic tool is located inside the Application panel in DevTools:

1. Open Google Chrome and navigate to the target web page you wish to audit.
2. Open DevTools by pressing F12 (Windows/Linux) or Cmd + Option + I (macOS).
3. Click the Application tab along the primary top navigation strip.
4. In the left sidebar, locate the Background services section.
5. Click on Back/forward cache.

Running an Automated bfcache Test

The Back/forward cache panel contains an automated testing utility designed to simulate real navigation cycles:

1. Inside the Back/forward cache panel, locate the Test back/forward cache button.
2. Click Test back/forward cache.
3. Chrome automatically navigates the tab away to a blank browser page (chrome://terms/) and immediately navigates back to your site.
4. During this round-trip transition, DevTools captures the exact browser lifecycle states and evaluates whether the page successfully restored from cache or triggered a full network reload.

Interpreting Test Results and Blocking Reasons

DevTools presents clear status reporting categorised into three primary classifications:

• Successfully restored from back/forward cache: Your page architecture complies fully with memory freezing specifications. Navigation back and forth will occur instantaneously for end users.
• Not restored from back/forward cache: Chrome highlights the precise reasons preventing caching under actionable categories:
  • Actionable: Factors directly remediable within frontend source code (e.g., presence of window.addEventListener('unload')).
  • Pending support: Features currently being worked on by the Chromium engine (e.g., active WebRTC or IndexedDB connections).
  • Not actionable: Factors dictated by intentional architectural constraints (e.g., explicit Cache-Control: no-store HTTP response headers).

Auditing and Resolving Common bfcache Blockers

When DevTools identifies blocking factors, apply these engineering resolutions:

• Replace the ‘unload’ Event: The unload event listener is deprecated because its execution guarantees are unreliable on mobile browsers and it strictly prevents bfcache entry. Replace all instances with the modern pagehide event listener:

  // Deprecated pattern (blocks bfcache)
  window.addEventListener('unload', () => { /* save state */ });
  
  // Modern replacement (bfcache compatible)
  window.addEventListener('pagehide', (event) => {
    if (event.persisted) {
      // Page is entering bfcache
    }
  });

• Close Open WebSockets and IndexedDB Transactions: An active WebSocket, WebRTC data channel, or uncommitted IndexedDB transaction blocks serialization. Listen for pagehide to close open connections, and re-establish them on pageshow when event.persisted is true.
• Audit Cache-Control Headers: If your web server emits Cache-Control: no-store, modern browsers respect this privacy instruction and refuse to retain memory snapshots. Reserve no-store exclusively for sensitive pages containing personal financial or authentication data.

Emulating Frame Eviction and Background Lifecycles

In mobile environments, browsers evict cached pages if device memory runs low. In the Back/forward cache panel, you can evaluate how your application handles sudden memory purges by toggling Evict from back/forward cache in the options strip, ensuring state restoration fallbacks trigger cleanly.