User experience plays a crucial role in the success of any website or web application. Users expect websites and applications to load quickly and respond to their interactions promptly. However, if your website or application has a high total blocking time, it can significantly drag down the user experience, leading to frustration, abandonment, and loss of potential customers.

So, what exactly is total blocking time? In web performance analysis, total blocking time (TBT) refers to the total duration of time between the first moment a user interacts with a web page (e.g., clicking a button or tapping a link) and when the browser is able to respond to that interaction. It includes the time taken by the browser to execute JavaScript code, which can potentially block the main thread and delay other critical tasks, such as rendering and input responsiveness.

Total blocking time is typically measured using various web performance metrics, such as First Input Delay (FID) and Cumulative Layout Shift (CLS), which are part of the Core Web Vitals, a set of performance metrics introduced by Google. 

FID measures the delay between the user's first interaction and the browser's response, while CLS measures the amount of unexpected layout shifts that occur during the loading process. Both FID and CLS contribute to the overall total blocking time and can impact the user experience.

High total blocking time can have several negative effects on user experience. Let's take a look at some of the key ways in which a high TBT can drag down your user experience:
 

Slow Interactions: 

When users interact with a website or web application, they expect an immediate response. However, if the browser is busy executing JavaScript code and the main thread is blocked, the website or application may not respond promptly to user interactions. 

This can result in slow or unresponsive buttons, forms, or other interactive elements, leading to frustration and poor user experience.

Delayed Content Rendering: 

Content rendering is a critical aspect of web performance. Users expect to see content appearing on the screen as quickly as possible. However, if the browser is blocked by JavaScript execution, it may delay the rendering of content, leading to a blank or incomplete page. 

Users may have to wait longer for the content to load, which can negatively impact their perception of the website or application and result in higher bounce rates.

Poor Mobile Experience: 

Mobile devices are becoming the primary means of accessing the internet for many users. However, mobile devices often have limited processing power and slower network connections compared to desktops. 

If a website or web application has a high total blocking time, it can be particularly detrimental to the mobile user experience, as the limited resources of mobile devices can exacerbate the performance issues, resulting in slower load times, unresponsive interactions, and frustrated users.

Lower Engagement and Conversions: 

Users have a limited attention span and high expectations when it comes to website performance. If a website or application takes too long to respond to user interactions, users may lose interest, abandon the site, and move on to a competitor's site. 

High total blocking time can result in lower user engagement, reduced time on site, and ultimately lower conversion rates, which can impact the success of an online business.

Negative SEO Impact: 

In addition to user experience, total blocking time can also impact search engine rankings. Google has indicated that web performance is a factor in its search ranking algorithm, and websites with poor performance may be penalized with lower rankings. 

High total blocking time can lead to lower search engine rankings, reduced organic traffic, and decreased visibility, which can have a significant impact on a website's overall performance and success.

In conclusion, total blocking time is a critical factor that can affect the user experience of a website or web application. A high TBT can result in slow interactions, delayed content rendering, poor mobile experience, lower engagement and conversions, and even negative SEO impact. Users expect websites and applications to load quickly and respond promptly to their interactions, and a high total blocking time can lead to frustration, abandonment, and loss of potential customers