# The Request / Response Pattern

A web request and its response are simple text messages, each made of a header and an optional body.

Journeyman · REST API · Updated October 29, 2026

Tools such as Postman, Insomnia and Visual Studio's `.http` files are great for testing API methods: they let us write requests, send them, save them, and run them again.

But the web request/response pattern behind them is a simple pattern. A request is just a simple text message that is sent to another computer over a network, and a response is a simple text message reply. Both messages consist of only two parts: 1) a header and 2) a body.

## Header

The header is like information on the outside of a letter. It provides the information needed to send the letter, including the mailing address, and postage stamp.

![Mailing address and stamp of a letter](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/fadecc34bf38454683580aa6dfe80e18.png "Mailing address and stamp of a letter")

The header of a request includes any information that is needed to send our request to the web server. Header information can include:

- **HTTP Verb:** The type of request GET, POST, PUT, DELETE
- **URL:** The "mailing address" of the request
- **Content-Type:** this describes the format of the contents of the request (the body)
- **Authorization:** this is a token that acts like an id card to verify your identity

```http
GET http://localhost:8080/api/categories
```

The first line of a request header must include the HTTP Verb and the URL. This is the only line that is required.

The number after `localhost:` is the port your API listens on. It's 8080 here, and yours may be different: a C# project's port is in `Properties/launchSettings.json`, and a Spring Boot app uses 8080 unless `server.port` in `application.properties` sets another.

## Body

Both the `Request` and `Response` can contain a body, but they are not required. If the `Request` does not include a body, then the header should provide all of the information the server needs.

![The contents of an envelope](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/b59fbe6cfb1548bc98fc0b7350d71e80.png "The contents of an envelope")

The body is like the contents of an envelope or package. For instance, if we want to add a new category to the database, the body contains all of the information about the new category. Adding a new category requires a POST request.

```http
POST http://localhost:8080/api/categories
Content-Type: application/json

{
  "categoryName": "Sports Equipment",
  "description": "All outdoor sports"
}
```

Note that the header includes an additional line describing the body format. The header ends when an empty line is encountered, and the body begins on the following line.

## Key terms

- [Request](https://www.ask-codey.com/glossary/request)
- [Response](https://www.ask-codey.com/glossary/response-web-development)
- [Header](https://www.ask-codey.com/glossary/header-web-development)
- [Request Body](https://www.ask-codey.com/glossary/request-body-web-development)

Source: https://www.ask-codey.com/lessons/dissecting-the-request-and-response-the-request-response-pattern