How to leverage browser caching for better Lighthouse results

How Browser Caching Works

When a user visits a web page for the first time, their browser sends a request to the server to fetch the required resources, such as HTML, CSS, JavaScript, and images. Instead of re-requesting these resources every time the user revisits the page, the browser can save a local copy of these files. This process, known as caching, allows the browser to quickly display the cached resources when the user returns to the page, significantly reducing load times and providing a more seamless browsing experience. The web server specifies cache control policies using HTTP headers, such as Cache-Control and Expires, to dictate how long the browser should store the cached resources and when to revalidate them. When the cache duration expires, the browser will re-fetch the resources from the server to ensure that the user sees the most up-to-date content.

Server-side Caching vs. Client-side Caching

Caching can be broadly classified into two categories: server-side caching and client-side caching.

Server-side caching involves storing copies of web pages or parts of web pages on the server. This process reduces the server’s workload, as it can serve pre-generated content to the client instead of dynamically generating it each time a user requests the page. Common server-side caching techniques include full-page caching, fragment caching, and object caching.

Client-side caching, on the other hand, refers to the storage of resources on the user’s device, such as in their browser cache. As mentioned earlier, this technique enables the browser to quickly display the cached resources when the user revisits a page, reducing load times and bandwidth usage. Client-side caching includes browser caching, application caching, and service worker caching.

Benefits of Caching

Caching offers several advantages for both users and website owners, including:

1. Faster load times: By storing resources locally, caching significantly reduces the time it takes to load a web page, providing a more seamless and enjoyable browsing experience.
2. Reduced server load: Caching reduces the number of requests made to the server, which decreases server load and allows it to handle more users simultaneously.
3. Lower bandwidth consumption: Since cached resources are served from the user’s device instead of being fetched from the server, caching reduces the amount of data transmitted over the network, resulting in lower bandwidth consumption and costs.
4. Improved SEO: Search engines, such as Google, consider page load times as a ranking factor. Faster-loading websites are more likely to rank higher in search results, driving more organic traffic to the site.

Limitations of Caching

Despite its numerous benefits, caching does come with certain limitations:

1. Stale content: If caching policies are not configured correctly, users may be served outdated content, leading to a suboptimal experience.
2. Complexity: Implementing and managing caching can be complex, particularly for websites with dynamic content or personalized user experiences.
3. Storage limitations: Browsers have limited storage capacity for caching, and older or less frequently accessed resources may be removed to make room for newer content. In the following sections, we will delve deeper into various caching strategies and provide practical tips on how to effectively leverage browser caching to improve Lighthouse results and enhance website performance.

Using Lighthouse to Check Caching Performance

Lighthouse is an open-source tool by Google that can evaluate a website’s performance, accessibility, SEO, and best practices. It also provides detailed information on how well your website is leveraging browser caching. To analyze your website’s caching performance with Lighthouse, follow these steps:

1. Open Google Chrome and navigate to your website.
2. Open Chrome Developer Tools by right-clicking on the page and selecting ‘Inspect’, or by pressing Ctrl + Shift + I (Windows) or Cmd + Option + I (Mac).
3. Click on the ‘Lighthouse’ tab.
4. Choose the categories you want to evaluate, making sure ‘Performance’ is selected.
5. Click on the ‘Generate report’ button. Once the report is generated, you can review the caching-related metrics under the ‘Performance’ category. Key metrics to look for include:

• Serve static assets with an efficient cache policy: This metric highlights resources that have a short cache TTL (Time To Live) or are not being cached at all. Optimizing the cache policies for these resources can improve load times and overall performance.
• Cache hit ratio: This ratio represents the percentage of requests that are served from the cache instead of being fetched from the server. A higher cache hit ratio indicates more efficient caching.
• Total byte weight: This metric shows the overall size of the resources on your website. Reducing the byte weight can help improve caching efficiency and page load times.

Using Google PageSpeed Insights to Analyze Caching

Google PageSpeed Insights is another valuable tool that can help you analyze your website’s caching performance. To use PageSpeed Insights, follow these steps:

1. Go to the Google PageSpeed Insights website.
2. Enter your website’s URL in the input field and click ‘Analyze’.
3. Once the analysis is complete, review the ‘Opportunities’ and ‘Diagnostics’ sections for caching-related suggestions. Key caching-related suggestions to look for include:

• Serve static assets with an efficient cache policy: Similar to Lighthouse, this suggestion identifies resources with short cache TTL or resources that are not being cached.
• Eliminate render-blocking resources: This suggestion highlights resources that are blocking the initial rendering of the page. Implementing proper caching for these resources can help improve page load times.

Interpreting the Results

After analyzing your website’s caching performance using Lighthouse and Google PageSpeed Insights, you should have a better understanding of your current caching strategy and areas for improvement. To optimize your caching strategy, focus on the following:

1. Implement efficient cache policies for static assets, such as images, stylesheets, and scripts.
2. Optimize the cache hit ratio by adjusting the cache TTL to balance between serving fresh content and minimizing server requests.
3. Reduce the total byte weight of your website’s resources to improve caching efficiency and load times. By addressing these issues, you can enhance your website’s performance and achieve better Lighthouse results. In the next section, we will discuss practical tips on how to optimize browser caching for improved website performance.

Best Practices for Configuring Caching Headers

Proper configuration of caching headers is crucial for optimizing browser caching performance. The following best practices will help you achieve efficient caching:

1. Leverage Cache-Control header: The Cache-Control header provides granular control over caching behavior. Use it to define cache directives, such as public, private, max-age, no-cache, and no-store. For example, to cache a resource for one month, set the header as Cache-Control: public, max-age=2592000.
2. Use Expires header as a fallback: The Expires header specifies an absolute expiration date for a resource. Although Cache-Control is preferred, some older browsers may not support it. In such cases, use the Expires header as a fallback to ensure proper caching behavior.
3. Enable ETag header for validation: The ETag header assigns a unique identifier to a resource, allowing browsers to check if a cached version is still valid. When a resource is updated, the ETag value changes, prompting the browser to fetch the updated version from the server.

Setting Caching Headers on Your Web Server

The process of setting caching headers varies depending on the web server you are using. Here are the steps to configure caching headers on some popular web servers:

<IfModule mod_expires.c> ExpiresActive On ExpiresDefault "access plus 1 month" Header append Cache-Control "public" </IfModule>

<IfModule mod_expires.c> ExpiresActive On ExpiresByType image/jpg "access plus 1 year" ExpiresByType image/png "access plus 1 year" ExpiresByType text/css "access plus 1 month" ExpiresByType application/javascript "access plus 1 month" </IfModule>

location ~* .(jpg|jpeg|png|gif|ico|css|js)$ { expires 30d; add_header Cache-Control "public"; }

Configuring Caching for Different Types of Assets

Different types of assets may require different caching configurations to ensure optimal performance. Here are some tips for configuring caching for various assets:

• Images: Images typically do not change frequently and can be cached for longer periods. Set a longer max-age value, such as 1 year, for image formats like JPEG, PNG, GIF, and SVG.
• Scripts and stylesheets: CSS and JavaScript files may be updated more frequently than images, so it is advisable to set a shorter max-age value, such as 1 month. However, if your scripts and styles

Testing Caching Performance with Lighthouse

To evaluate the effectiveness of your caching optimizations, generate a new Lighthouse report following the steps mentioned in the ‘Analyzing Your Current Caching Strategy’ section. Compare the new report with the previous one, focusing on the following caching-related metrics:

• Serve static assets with an efficient cache policy: Check if the number of resources with short cache TTL or no caching has decreased. This indicates that your cache policy optimizations have been effective.
• Cache hit ratio: A higher cache hit ratio in the new report suggests more efficient caching, resulting in fewer server requests and faster load times.
• Total byte weight: If the total byte weight has decreased, it means that your caching optimizations have reduced the overall size of your website’s resources, improving caching efficiency and load times.

Using Other Tools to Test Caching Performance

In addition to Lighthouse, you can use the following tools to verify your caching performance:

1. Google PageSpeed Insights: Rerun the PageSpeed Insights test for your website and compare the new results with the previous ones. Look for improvements in caching-related suggestions, such as “Serve static assets with an efficient cache policy” and “Eliminate render-blocking resources.”
2. WebPageTest: WebPageTest is another useful tool for testing caching performance. Run a test on your website and examine the “Effective use of CDN” and “Cache static content” grades under the “Performance Results” section. Improvements in these grades indicate better caching performance.

Interpreting and Troubleshooting Caching Results

When evaluating your caching performance, consider the following tips:

1. Set realistic expectations: Although optimizing browser caching can significantly improve your website’s performance, it may not resolve all performance issues. Some aspects, such as server response times and render-blocking resources, may require additional optimizations.
2. Identify problem resources: If you still notice resources with inefficient caching in the Lighthouse or PageSpeed Insights reports, investigate their cache policies and server configurations to identify any issues.
3. Check for third-party resources: Some resources, such as third-party scripts and fonts, may not have optimal caching policies. While you have limited control over these resources, consider hosting them locally or using alternative solutions that offer better caching options.
4. Consider advanced caching strategies: If you have already implemented basic caching optimizations but still need to improve performance, consider adopting advanced strategies like cache versioning, service workers, or edge caching. By testing, interpreting, and troubleshooting your caching performance, you can ensure that your browser caching optimizations have the desired effect on your website’s performance, ultimately resulting in better Lighthouse scores and an improved user experience.