What is Total Blocking Time and How to Improve It?
Total Blocking Time (TBT) is a crucial metric for website performance, particularly for user experience. It measures the amount of time a page is unresponsive to user input, including clicks, scrolls, and keyboard inputs. This delay affects the user’s perception of website speed and responsiveness, leading to a poor user experience. In this article, we will discuss what Total Blocking Time is, how it affects website performance, and what steps you can take to improve it.
Understanding Total Blocking Time
Total Blocking Time measures the amount of time a web page is unresponsive to user input. It is calculated as the sum of all blocks longer than 50ms during page load. A block is any period of time where the main thread is busy with tasks that prevent user input from being processed. TBT includes delays caused by JavaScript execution, rendering, layout shifts, and other factors.
Why Total Blocking Time Matters
Total Blocking Time has a significant impact on user experience. Websites with high TBT values often feel slow and unresponsive, leading to frustration and lower engagement rates. A high TBT also affects search engine rankings since it is a key metric in Google’s Core Web Vitals, which measures website performance and user experience.
How Total Blocking Time is Measured
Total Blocking Time is measured using performance metrics tools such as Lighthouse, PageSpeed Insights, or WebPageTest. These tools simulate a user’s experience and provide data on page speed and user experience metrics, including Total Blocking Time.
Factors Affecting Total Blocking Time
Several factors can impact Total Blocking Time. Identifying these factors is crucial to improving TBT and optimizing website performance. Here are some of the main factors affecting TBT:
– JavaScript Execution Time
JavaScript is a scripting language used to create interactive web pages. However, excessive JavaScript can cause delays in page load and increase TBT. Optimizing JavaScript code, reducing the number of scripts, or deferring non-critical scripts can help reduce TBT.
– Render Time
Render time refers to the time it takes to generate the visual layout of a web page. Render-blocking resources such as CSS or JavaScript can delay render time and increase TBT. Optimizing resource delivery, using minified CSS and JavaScript, and leveraging browser caching can help improve render time and reduce TBT.
– Layout Shifts
Layout shifts occur when page content moves or shifts unexpectedly, causing visual instability and increasing TBT. Addressing layout shift issues, optimizing images and videos, and avoiding or deferring non-critical page elements can help reduce TBT.
Now that we have identified the main factors affecting Total Blocking Time, here are some steps you can take to improve TBT and optimize website performance:
– Reduce JavaScript Execution Time
As we mentioned earlier, JavaScript can significantly impact TBT. To reduce JavaScript execution time, you can:
- Minify JavaScript code to reduce its size and load time.
- Defer non-critical scripts to load them after the main content.
- Eliminate unused JavaScript to reduce the amount of code that needs to be executed.
– Optimize Render Time
To optimize render time and reduce TBT, you can:
- Minimize the use of render-blocking resources such as CSS and JavaScript.
- Use asynchronous loading for non-critical resources.
- Leverage browser caching to store resources locally and reduce the need for multiple requests.
– Address Layout Shifts
To address layout shift issues and reduce TBT, you can:
- Optimize images and videos to reduce their size and improve loading times.
- Avoid or defer non-critical page elements such as social media widgets or ads.
- Use responsive design to ensure that pages adjust to different screen sizes without causing layout shifts.
– Limit Third-Party Scripts
To limit the impact of third-party scripts on TBT, you can:
- Limit the number of third-party scripts used on your website.
- Defer third-party scripts to load them after the main content.
- Use asynchronous loading for non-critical third-party scripts.
– Optimize Resource Sizes
To optimize resource sizes and reduce TBT, you can:
- Compress images, videos, and other resources to reduce their size.
- Use formats such as WebP or AVIF that offer better compression than traditional formats.
- Leverage browser caching to store resources locally and reduce the need for multiple requests.
By implementing these steps, you can significantly improve Total Blocking Time and optimize your website’s performance and user experience.
Conclusion
Total Blocking Time is a critical metric for website performance and user experience. By understanding its impact and identifying the factors that affect it, you can take steps to improve TBT and optimize your website’s performance. Implementing best practices such as reducing JavaScript execution time, optimizing render time, addressing layout shifts, limiting third-party scripts, and optimizing resource sizes can help you achieve lower TBT values and improve user experience.
FAQs
1. What is Total Blocking Time (TBT)?
Total Blocking Time measures the amount of time a page is unresponsive to user input during page load, including clicks, scrolls, and keyboard inputs.
2. Why does Total Blocking Time matter?
Total Blocking Time has a significant impact on user experience and search engine rankings. Websites with high TBT values often feel slow and unresponsive, leading to frustration and lower engagement rates.
3. How can I measure Total Blocking Time?
Total Blocking Time can be measured using performance metrics tools such as Lighthouse, PageSpeed Insights, or WebPageTest.
4. What factors affect Total Blocking Time?
Several factors can impact Total Blocking Time, including JavaScript execution time, render time, layout shifts, third-party scripts, and large or unoptimized resources.
5. How can I improve Total Blocking Time?
To improve Total Blocking Time, you can take steps such as reducing JavaScript execution time, optimizing render time, addressing layout shifts, limiting third-party scripts, and optimizing resource sizes.