What is Query String

A query string is a set of parameters included in an HTTP request that enables the passing of information from one page to another. It consists of a series of key-value pairs appended to a specific URL. The query string is specified by the values following the ? (question mark) in the URL, with each parameter separated by an ampersand (&) symbol.

The purpose of the query string is to provide additional data to the receiving page, allowing it to process and respond accordingly. The receiving page can access and utilize the information from the query string to customize its behavior or display specific content based on the provided parameters.



How to create a Query String ?

To create a new writable instance of HttpValueCollection, you can use the System.Web.HttpUtility.ParseQueryString(string.Empty) method. This method allows you to parse an empty query string and obtain a new HttpValueCollection object that can be modified to add or remove parameters.

By passing an empty string (string.Empty) as the parameter to ParseQueryString, you initialize a new HttpValueCollection without any existing query parameters. This provides you with a clean slate to populate the collection with the desired key-value pairs.

Once you have the HttpValueCollection instance, you can use its methods and properties to manipulate the query parameters, such as adding new parameters using the Add method or retrieving values using the indexer notation.

NameValueCollection queryString = System.Web.HttpUtility.ParseQueryString(string.Empty); queryString["param1"] = "paramValue1"; queryString["param2"] = "paramValue2";

Note that HttpValueCollection is a specialized collection class designed to handle URL-encoded key-value pairs, commonly used in query strings.

How to retrieve Query String ?

The QueryString collection retrieves the values of the variables in the HTTP query string and it is specified by the values following the ? (question mark).

protected void Page_Load(object sender, EventArgs e) { string param1 = Request.QueryString["param1"]; string param2 = Request.QueryString["param2"]; }

Query String - limitations

Query strings do have certain limitations that are important to consider. One limitation is the length constraint imposed on query strings. Web browsers and servers have specific limits on the maximum length of a URL, including the query string. If you need to send a large amount of information, exceeding these limits, using query strings may not be a feasible option.

Another limitation of query strings is their lack of security. Since query string data is appended to the URL and is visible to users, it can be easily manipulated by malicious users. This raises potential security concerns as sensitive information or parameters can be tampered with, leading to unauthorized access or incorrect data processing. To mitigate these risks, it is essential to properly validate and sanitize query string parameters on the server side and implement appropriate security measures, such as encryption or authentication mechanisms, depending on the sensitivity of the data being passed.

Considering these limitations, it is important to evaluate the nature of the data being transmitted and the security requirements of your application when deciding whether to use query strings or alternative methods for data transmission and retrieval.


It is important to note that the ? (question mark) used to separate the URL from the query string is not considered part of the query string itself. Instead, it serves as a delimiter to indicate the start of the query string portion of the URL.