What Are Query Parameters? Definition and Examples

Query parameters are the hidden switches that tell a website what content to show—without changing the page you’re on. Every time you see a question mark followed by extra text in the address bar, you’re passing key‑value pairs that shape the response.

Bottom line: Query parameters — key‑value pairs after the “?” · Standard: RFC 3986 (URI) · Typical max length: ~2048 characters · Separator: &

What are query parameters in a URL?

Query parameters (also called URL parameters or query strings) are key‑value pairs appended after a question mark. They allow the client to pass extra data to the server without changing the resource path. The server then uses these values to filter, sort, or customize the response.

How do query parameters work?

• They follow the ? in a URL: ?key1=value1.
• Multiple pairs are separated by &.
• They are defined by RFC 3986 as part of the URI query component.
• Servers access them via $_GET (PHP), req.query (Node.js), etc.

“When you call a REST API, you often see something like ?page=2&limit=10 to paginate results.” – Moesif

What is a query parameter in REST API?

In REST APIs, query parameters are used to refine or filter the resource being requested. They are optional and appear after the endpoint URL. For example, GET /users?role=admin returns only admin users.

What are query parameters in API?

APIs use query parameters to control pagination (?page=1&limit=20), sorting (?sort=name), and filtering (?category=books). They are distinct from path parameters which identify a specific resource.

How to write a query parameter?

Writing a query parameter is straightforward but requires encoding of special characters.

What is the syntax of a query string?

1. Start with ? after the base URL.
2. Write key=value for the first parameter.
3. Add & before each additional pair.
4. Encode keys and values using percent‑encoding (e.g., space → %20 or +).

Example: ?search=hello%20world&lang=en

How to encode special characters in query parameters?

Reserved characters such as ?, &, =, # must be percent‑encoded. Use URLSearchParams in JavaScript or urllib.parse.urlencode in Python.

How to handle multiple values for the same key?

Some frameworks support repeating keys: ?color=red&color=blue. Others expect array notation: ?color[]=red&color[]=blue. Behavior is server‑dependent.

What is an example of a query parameter?

Real‑world examples show how query parameters control every web interaction.

Common examples from Google Search URLs

Google uses ?q=query+parameters for search. The q parameter contains the entered keywords.

Example in a REST API call

“A typical REST API endpoint like https://api.example.com/articles?author=kay&limit=10 uses query parameters to filter and limit results.” – Moesif

Example of pagination using query parameters

?page=2&limit=10 requests the second page of ten items.

What is the difference between a URL and a query parameter?

The confusion often comes from using “URL” and “query parameter” as if they were alternatives. They are not.

URL parameters vs query parameters

“URL parameter” is a broad term that includes both path parameters and query parameters. “Query parameter” refers specifically to the key‑value pairs after ?.

Path parameters vs query parameters in REST APIs

The implication: Use path parameters when the value is essential to identify the resource; use query parameters for optional refinements.

When to use query parameters vs path parameters

If the parameter identifies a unique entity (e.g., user ID), use a path parameter. If it refines a collection (e.g., search term, page number), use a query parameter.

How to pass query parameters in URL?

Passing query parameters correctly ensures your request is interpreted as intended.

Passing multiple query parameters

1. Start with ?.
2. Write the first pair: key1=value1.
3. Append & and the next pair: &key2=value2.
4. Continue for all parameters.

Example: https://example.com/search?q=cats&sort=price_asc&page=2

Using the question mark and ampersand

The question mark signals the start of the query string. The ampersand separates individual parameters.

How to build query strings programmatically (JavaScript, Python)

In JavaScript: new URLSearchParams({key: 'value'}).toString()
In Python: urlencode({'key': 'value'})

The catch: Query strings are visible in browser history, server logs, and referrer headers — never pass passwords or tokens this way.

FAQ