What is cURL?

cURL is a powerful, command-line tool used to transfer data to and from servers, making it an excellent choice for web hosting customers to test and troubleshoot their websites. It supports various protocols, including HTTP and HTTPS, allowing you to interact directly with your website’s server. One key advantage of cURL is that it does not use a client-side cache, ensuring that the data you retrieve is the latest version directly from the server. This makes cURL ideal for verifying server responses, checking website functionality, or diagnosing issues without interference from cached content.

In this article, we’ll guide you through using cURL to test your website and explain three common flags: -v, -i, and -k. These flags will help you gather detailed information, view headers, or bypass SSL verification when troubleshooting.

Getting started with cURL

cURL is typically pre-installed on Linux and macOS systems. For Windows, you can use it via the Command Prompt, PowerShell, or install it through tools like Git Bash or Windows Subsystem for Linux (WSL). To check if cURL is installed, open your terminal or command prompt and type:

curl --version

If installed, this will display the cURL version. If not, you can download it from the official cURL website or install it using your system’s package manager (e.g., sudo apt install curl for Ubuntu).

To test your website, you can run a basic cURL command by entering:

curl https://yourwebsite.com/

This retrieves the HTML content of your website’s homepage directly from the server. Since cURL doesn’t cache responses, you’re guaranteed to see the latest data, which is critical for troubleshooting issues like outdated content or server misconfigurations.

Common cURL flags for troubleshooting

Below, we’ll cover three commonly used cURL flags to help you test and diagnose issues with your website.

-v (Verbose mode)

The -v flag enables verbose mode, which provides detailed information about the request and response, including headers, connection details, and SSL handshakes. This is particularly useful for debugging server issues or verifying how your website responds to requests.

Example:

curl -v https://yourwebsite.com/

What it does:

• Displays the full communication process, including the request sent to the server and the response received.
• Shows headers (e.g., Content-Type, Server), connection details, and any errors (e.g., 404 or 500 status codes).
• Helps identify issues like redirects, SSL errors, or server misconfigurations.

Use case: If your website isn’t loading as expected, the verbose output can reveal whether the server is responding correctly or if there’s an issue with DNS, redirects, or server errors.

-i (Include headers)

The -i flag includes the HTTP response headers in the output, along with the webpage content. This is useful for checking metadata like status codes (e.g., 200 OK, 404 Not Found), content types, or caching instructions without the extra detail provided by -v.

Example:

curl -i https://yourwebsite.com/

What it does:

• Shows the HTTP headers (e.g., HTTP/1.1 200 OK, Content-Type: text/html) followed by the webpage’s content.
• Allows you to verify server responses, such as whether the correct content type is being served or if redirects are occurring.

Use case: Use this flag to quickly check if your server is returning the expected status code or headers, such as confirming that a page is being served as text/html or diagnosing redirect issues.

-k (Insecure Mode)

The -k flag allows cURL to bypass SSL/TLS certificate verification, which can be helpful when troubleshooting websites with invalid or self-signed SSL certificates (common in staging or development environments).

Example:

curl -k https://yourwebsite.com/

What it does:

• Ignores SSL certificate errors, allowing cURL to connect to the server even if the certificate is invalid, expired, or self-signed.
• Retrieves the webpage content as it would with a valid certificate.

Use case: If you’re testing a development site with a self-signed certificate and cURL fails with an SSL error, use -k to bypass the error and retrieve the content. Use this flag cautiously, as it reduces security by ignoring certificate validation. Avoid using it on production sites.

Why cURL’s lack of cache matters

Unlike web browsers, cURL does not store a client-side cache. When you make a request with cURL, it always fetches the latest data directly from the server. This is particularly valuable when troubleshooting issues like:

• Verifying that recent changes to your website (e.g., updated CSS or HTML) are live.
• Checking if server-side configurations, like caching rules or redirects, are working as expected.
• Diagnosing issues where a browser might show outdated content due to its cache.

By using cURL, you can be confident that the response reflects the server’s current state, making it a reliable tool for testing and debugging.

Best practices and next steps

• You can use multiple flags together, such as curl -vi https://yourwebsite.com, to see both verbose output and headers.
• Test specific pages: Replace https://yourwebsite.com with specific URLs (e.g., https://yourwebsite.com/about) to troubleshoot individual pages.
• Check for errors: Pay attention to status codes (e.g., 200 for success, 404 for not found, 500 for server errors) in the output to diagnose issues.
• Secure your production environment: Avoid using -k on live websites, as it bypasses important security checks.

If you encounter persistent issues, such as 500 errors or SSL problems, contact Liquid Web’s support team for assistance. You can also explore additional cURL options, like -X for custom HTTP methods (e.g., POST) or -H to add custom headers, for more advanced troubleshooting.