Explainer1 min readUpdated July 1, 2026

What is a query string?

Short answer

A query string is the portion of a URL after the ? that passes data as key=value pairs joined by &. For example ?page=2&sort=new sends two parameters: page and sort.

Where the query string sits

In a URL, the query string starts at the ? and runs to the end (or to a # fragment). It carries parameters the page or API uses. See the anatomy of a URL for the full structure.

https://example.com/search?q=cats&page=2
                          |________________|
                             query string

A query string with two parameters

How it is structured

A ? marks the start of the query string
Each parameter is a key=value pair
Pairs are separated by &
Values with spaces or symbols are percent-encoded (a space becomes %20)
The same key can repeat, e.g. ?tag=a&tag=b

Try it: Query Param BuilderBuild and edit query parameters, correctly encoded, without hand-typing.Open tool

Encode values, not the whole stringReserved characters inside a value must be percent-encoded so they are not mistaken for delimiters. See how to URL encode.

What query strings are used for

Search terms, filters, sorting, and pagination
Tracking parameters like UTM tags
Passing non-sensitive state between pages
API request options

References

Questions

What is the difference between a query string and a path?

The path identifies which resource or page you want (/search). The query string, after the ?, carries parameters that modify or filter it (?q=cats). The path is hierarchical; the query string is key-value data.

Is data in a query string secure?

No. Query strings are visible in the address bar, browser history, and server logs. Never put passwords or secrets in them; use them only for non-sensitive parameters.

Does the query param builder upload my URL?

No. Parameters are built and encoded entirely in your browser tab. Nothing is uploaded or stored.

Keep reading

Explainer1 min readThe anatomy of a URLEvery URL is made of parts: scheme, host, port, path, query, and fragment. Here is what each piece does, with a labelled example.Read

Guide1 min readHow to build a query stringA query string passes parameters in a URL. Here is how to format key/value pairs, encode values, and handle repeated keys correctly.Read

Explainer1 min readWhat are UTM parameters?UTM parameters are tags added to a URL so analytics can tell where traffic came from. Here are the five parameters and how to use them consistently.Read