What is the Common Gateway Interface?

Common Gateway Interface is an interface specification used to execute user HTTP requests based on external programs on web servers. Read this article to learn about its importance in web development.
authorImageVarun Saharawat30 Oct, 2025
What is the Common Gateway Interface?

A Common Gateway Interface (CGI) is a standard for connecting external applications with a server database. It defines a set of rules that define how web servers can communicate or process a user’s HTTP request with the executable programs running on the server. It acts as a communication bridge between the web servers and information sources over the server. Let us know about the role of a common gateway interface in web development in this article.

What is a Common Gateway Interface (CGI)?

Common Gateway Interface is a specification used for processing user HTTP or HTTPS user requests to execute an external program on a web server. These external programs are known as CGI Script as they are scripting languages.  Consider a use case when a user submits a web form on the server that uses Common Gateway Interface (CGI). The user request is sent to the server in the form of an HTTP request. Now, the web server tries to find the CGI script in the database, and if it finds the script it responds to the web client with an HTTP response, usually in the form of HTML. 

Common Gateway Interface: Key Highlights

Some of the key features of CGI or Common Gateway Interface, are mentioned below.
  • Common Gateway Interface is a standard protocol developed for interfacing external applications with the web server.
  • It was developed at NCSA (National Center for Supercomputing Applications) in 1993.
  • It allows an external executable file to respond to a user’s HTTP or HTTPS request from the web browser.
  • The file extension in the CGI file is saved with a .cgi extension.
  • CGI is not a programming language. It is a simple protocol that is used to communicate web forms and external programs.
  • Common Gateway Interface is stored on a web server used to pass information to an external program from the web server.
  • It can use PERL, C, C++ as a scripting language. PERL is more frequently used as a scripting language with CGI. Let us check the format of a Perl CGI script below in the table.
Common Gateway Interface with Perl
print “Content-type: text/HTML\r\n\r\n” print ‘<html>’; print ‘<head>’; print ‘<title> CGI Script<title>’; print ‘</head>’; print ‘<body>’; print ‘</body>’; print ‘</html>’;

Roles of Common Gateway Interface in Web Development

Common Gateway Interface plays a significant role in web development by helping the execution of the scripts on the web server to display the output as web content in the form of an HTTP response. Some of the key roles of the common gateway interface are mentioned below.

1. Create Dynamic Content 

With the help of CGI script dynamic pages in response to user’s request can be generated. It can use various scripting language like Perl, Python, C, and C++ to process user requests. These scripts interact with the database and perform server-side scripting to create dynamic HTML content.

2. Server Side Scripting

Common Gateway Interface allows for server side scripting. Here, the script is first executed on the server side and then the result is displayed on the web client browser in the form of HTTP response. It allows for more complex and interactive web applications. 

3. Form Handling

The Common Gateway Interface is generally used to handle HTML form submissions on web pages. The data from the HTML form submitted by the user is sent to the server and processed, validated and then with the help of CGI Script response is generated. 

4. Interactivity 

The CGI Scripts can easily interact with the user. It processes data sent by the user, generates customized dynamic content based on the input given by the user. Also, for creating dynamic pages and web applications it is important to have interaction between the user and the CGI Script.

5. Flexibility

CGI supports a wide range of programming languages to allow developers to perform server-side scripting easily. Some of the popular scripting programming languages are Python, Perl, C, C++, etc which is used for CGI script and allow creativity and innovation in web development.

6. Integration with Database 

The Common Gateway Interface can easily interact with databases to retrieve crucial information based on the user's HTTP request. We can easily store and manage data to build dynamic websites.

7. Integration with Web Servers

CGI is supported on most of the web servers available nowadays which makes it widely accessible by developers. Popular web servers such as Apache, Ngnix, etc can be used to execute CGI scripts in response to the user's HTTP request. 

8. Easy Debugging and Testing 

With the help of CGI scripts, we can easily debug or test these scripts on the server, which allows easy troubleshooting issues and managing functionalities before deploying the application.

9. Scalability

CGI  is most frequently used to run scripts on web servers. However, it is not as scalable and efficient as modern approaches such as WSGI (Web Server Gateway Interface), FastCGI, etc. However, for medium or low-level applications Common Gateway Interface is most preferred. 

Working on Common Gateway Interface 

  • First, write CGI scripts to process users' requests and give the required output. You can easily access CGI Scripts on the URL https://xyz.com/cgi-bin/
  • Make sure your web server is configured and can recognize the directories in which CGI Script is present. 
  • When a client gives to access a file in the database within the CGI directory then HTTP servers run the script and present the output as a response on the client's browser.
  • The environment is set up on the web browsers with the information about the client's request.
  • GET and Post are two methods which are used by web browsers and web servers to communicate. 
  • The GET method is a little less secure as it can be viewed by anyone while the POST method is a secure method to transfer data.

Advantages of Common Gateway Interface (CGI)

Some of the major benefits of using CGI script for the web servers are given below.
  • It is easy to execute a CGI Program to process a user HTTP request.
  • It helps web servers and web browsers to communicate easily.
  • It is frequently used to create dynamic web content based on the CGI Script.
  • It support various programming languages which makes it more flexible and efficient.
  • It is supported on multiple web servers such as Apache, Nigix, etc. 
  • It supports server-side scripting.
  • It can easily interact with a database to modify contents or access information.

Disadvantages of Common Gateway Interface (CGI)

Some major demerits of using the Common Gateway Interface are mentioned below.
  • It does not provide data integrity and sensitive information can be leaked as it is vulnerable to cyber-attacks.
  • They are slow when users attempt multiple requests. Some of the effective approaches that can be used for large requests or applications are WSGI (Web Server Gateway Interface), FastCGI, Django, Flask, etc. 
  • It does not consist of pre-defined frameworks.

Skills Required for Common Gateway Interface

The Common Gateway Interface supports many programming languages and is language independent which helps developers to write programs in any language and operate in multiple environments. However, some of the popular scripting languages which you can learn to perform CGI Scripting are PHP, Perl, C, Python, C++, etc.

Who Should Learn Common Gateway Interface Technologies?

The three major developers who must have knowledge about CGI Scripts are given below.
    • Python Developers: Python Script can be used to interpret CGI Script easily by Python Developers. 
    • Android Developers: Android developers also must have knowledge of CGI scripts.
    • PHP Developers: PHP developers prepare PHP Code which is applied on the server side as modules in the web server and must support Common Gateway Interface.
  • Backend Developers: CGI must be relevant for a backend developer who works on server-side technologies or applications. Learning CGI will help them how to process client requests, execute scripts, and generate dynamic content.
  • Full Stack Developers: Full Stack Developers work on both frontend and backend applications. They can benefit from learning CGI as learning CGI will help them how to process client requests, execute scripts, and generate dynamic content. Also, they will be able to extract insights on how server-side technologies interact with client requests.

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Common Gateway Interface FAQs

What is the full form of CGI?

CGI Stands for Common Interface Gateway used to create dynamic content on web servers based on user HTTP requests.

What is the role of CGI in Web development?

CGI is used to generate dynamic content on web pages and provides an interface between the HTTP server and programs on web servers.

What is the extension of the CGI file?

The CGI file is saved by using the .cgi extension.

Why was the Common Gateway Interface introduced?

The Common Gateway Interface was introduced to execute user requests based on external programs which are also known as CGI programs or scripts. It helps in setting interaction with the HTTP Server requests and responses.