Mastering REST API Parameters: Best Practices for Query Strings

Guide: This article details the best practices for using parameters and query strings in REST API design.

When designing an API, the goal is to empower users rather than to showcase the service itself. Although HTTP verbs and resources allow programmers to interact, adding too many features makes the system cumbersome and hard to use.

A common pagination example: if a database contains millions of records, it is impossible to send every record to the client in a single response.

The solution is to use query strings, i.e., parameterization.

What is parameterization?

Generally, parameterization is a way to configure a request. In programming languages, a function can return a value without parameters; similarly, a REST API, being stateless, can operate without requiring prior context.

“Every REST interaction is stateless; each request contains all the information needed, independent of previous requests.” – REST API designer Fielding

HTTP provides several ways to add parameters to a request: query strings, POST bodies, PUT/PATCH requests, and HTTP headers, each with its own use cases and specifications.

The simplest way to include parameters is to use POST. Many APIs historically used POST to place parameters in the HTTP body, but such designs are less suitable for query operations.

Before designing, ask the right questions to avoid mistakes.

Question 1: What type of parameter are we adding?

We should first ask which type of parameter we need, referring to the definitions in the HTTP RFC.

The RFC defines many standard fields. While it is possible to invent new fields, using mature technologies is usually simpler. For example, GraphQL introduces concepts that seem radical from a REST perspective, but it has its own trade‑offs.

Using HTTP headers is a common practice: they can specify format or media type, indicate the desired response format, or convey API version (e.g., JSON vs. XML). Headers can also prevent browser caching, such as using Cache-Control: no-cache with a random query string.

Authorization can also be treated as a parameter. The HTTP RFC defines the Authorization header.

After reviewing all default fields, the next step is to decide whether to create custom fields for parameters or to place them in the query string.

(To be continued)