HTTP response headers provide essential details about the server's response, including status, caching, and security settings, playing a key role in diagnosing issues, optimizing performance, and enhancing security.

Understanding these headers aids in debugging, troubleshooting, and comprehending server response mechanisms to requests.

cURL, by default, displays only the response body but can also be configured to display the response headers, providing a comprehensive insight into server interactions.

Related: How to view HTTP request headers when using cURL
Related: How to add custom headers to cURL request

Steps to view HTTP response headers using cURL:

  1. Open the terminal or command prompt on your computer.
  2. Make a standard cURL request to a desired URL. 
    $ curl www.simplified.guide

<!DOCTYPE html>
<html lang="en">
<head>


    <meta charset="utf-8">
    <title> Simplified Guide </title>
##### snipped

    Note that only the response body or content is displayed.

  3. View the headers and the content using the -i or --include option. 
    $ curl -i www.simplified.guide
HTTP/1.1 200 OK
Date: Tue, 26 Sep 2023 08:36:01 GMT
Server: Apache
X-Powered-By: PHP/8.2.10
Vary: Cookie
Set-Cookie: DokuWiki=ka1l9l3j8d7i6rpj3ia3ppb13d; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: DW68700bfd16c2027de7de74a5a8202a6f=deleted; expires=Thu, 01 Jan 1970 00:00:01 GMT; Max-Age=0; path=/; HttpOnly
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8


<!DOCTYPE html>
<html lang="en">
<head>


    <meta charset="utf-8">
    <title> Simplified Guide </title>
##### snipped
  4. Only see headers and exclude the body using the -I or --head option. 
    $ curl -I www.simplified.guide
HTTP/1.1 200 OK
Date: Tue, 26 Sep 2023 08:36:46 GMT
Server: Apache
X-Powered-By: PHP/8.2.10
Vary: Cookie
Set-Cookie: DokuWiki=bin6f85ecq6bhlltr3vss3hm66; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: DW68700bfd16c2027de7de74a5a8202a6f=deleted; expires=Thu, 01 Jan 1970 00:00:01 GMT; Max-Age=0; path=/; HttpOnly
Content-Type: text/html; charset=utf-8
  5. View verbose output, including request and response headers, using the -v or --verbose option. 
    $ curl -v www.simplified.guide
*   Trying 127.0.0.1:80...
* Connected to www.simplified.guide (127.0.0.1) port 80 (#0)
> GET / HTTP/1.1
> Host: www.simplified.guide
> User-Agent: curl/8.1.2
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Tue, 26 Sep 2023 08:37:09 GMT
< Server: Apache
< X-Powered-By: PHP/8.2.10
< Vary: Cookie
< Set-Cookie: DokuWiki=3uod8b4v0n3fmvi1aj6r3c0vp0; path=/; HttpOnly
< Expires: Thu, 19 Nov 1981 08:52:00 GMT
< Cache-Control: no-store, no-cache, must-revalidate
< Pragma: no-cache
< Set-Cookie: DW68700bfd16c2027de7de74a5a8202a6f=deleted; expires=Thu, 01 Jan 1970 00:00:01 GMT; Max-Age=0; path=/; HttpOnly
< Transfer-Encoding: chunked
< Content-Type: text/html; charset=utf-8
<

<!DOCTYPE html>
<html lang="en">
<head>


    <meta charset="utf-8">
    <title> Simplified Guide </title>
##### snippped

    Verbose mode is particularly useful for debugging connections, certificate issues, or understanding the full transaction process.

  6. Save the headers to a file using the -o or --output option followed by the filename. 
    $ curl -I www.simplified.guide -o headers.txt
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

    This method is helpful when dealing with extensive headers or when you want to document server responses.

  7. Examine the saved request header file. 
    $ cat headers.txt
HTTP/1.1 200 OK
Date: Tue, 26 Sep 2023 08:40:00 GMT
Server: Apache
X-Powered-By: PHP/8.2.10
Vary: Cookie
Set-Cookie: DokuWiki=1t1e1l3gn9qnm37c0j7dj01hki; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: DW68700bfd16c2027de7de74a5a8202a6f=deleted; expires=Thu, 01 Jan 1970 00:00:01 GMT; Max-Age=0; path=/; HttpOnly
Content-Type: text/html; charset=utf-8
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