Daily Archives: 11 November 2023

Understanding the cURL Command for Performance Metrics

Breaking Down the Command

In the world of web development and network administration, the cURL command is a versatile tool used for transferring data using various protocols. One interesting application of this command is to measure the performance of a web server. Let’s dissect a specific cURL command to understand how it works:

curl -svo /dev/null -w "Connect: %{time_connect} \n TTFB: %{time_starttransfer} \n Total time: %{time_total} \n" https://bytefreaks.net/;

Components of the Command

  1. curl: This is the basic command call for using cURL, which initiates the data transfer.
  2. -sv: The -s flag stands for ‘silent’, which makes cURL less talkative by hiding the progress meter and error messages. The -v flag is for ‘verbose’, providing more information about the transaction. These flags might seem contradictory, but together, they suppress unnecessary details while keeping the essential info visible.
  3. /dev/null: This part redirects the output of the command to a special file that discards all data written to it. In essence, it’s used here to ignore the body of the response.
  4. -w: This flag is used to specify what data to display on the screen after the execution of the command. It stands for ‘write-out’.
  5. "Connect: %{time_connect} \n TTFB: %{time_starttransfer} \n Total time: %{time_total} \n": This is a formatted string that curl will use to display the timing statistics:
    • %{time_connect}: Shows the time it took to establish the connection to the server.
    • %{time_starttransfer}: Stands for ‘Time to First Byte’ (TTFB), indicating the time from the start until the first byte is received.
    • %{time_total}: Displays the total time taken for the operation.
  6. https://bytefreaks.net/: This is the URL to which the cURL request is made.

Practical Use

This command is particularly useful for testing the performance of web servers. By analyzing the connect time, TTFB, and total time, administrators and developers can get insights into potential bottlenecks or performance issues. For instance, a long TTFB might suggest server-side delays in processing requests.


The cURL command demonstrated here is a powerful tool for performance testing. It’s concise yet provides crucial metrics for understanding how a web server responds to requests. By mastering such commands, one can effectively monitor and optimize web server performance, ensuring better user experiences and efficient server management.