> For the complete documentation index, see [llms.txt](https://docs.langstack.com/welcome/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.langstack.com/welcome/get-started/learn-langstack/introduction-to-rest-api.md).

# Introduction to REST API

**Get familiar with REST APIs on Langstack. By the end of this section, you will acquire a deeper understanding of REST APIs, their creation, and their deletion.**

## What is Langstack API?

<figure><img src="https://media.langstack.com/documentation/media/images/code/training_manual/chapter_4/ch4apimenu.png" alt=""><figcaption></figcaption></figure>

* The API template is used to build an API (an application programming interface endpoint) to perform business user-defined logic.
* An API must have a base URL. A base URL is a text that is at the beginning of the URL, which consists of&#x20;
  * the customer URL
  * The text dataapi
  * Group name for the API&#x20;
  * API name
  * Path parameters&#x20;

<figure><img src="https://media.langstack.com/documentation/media/images/code/training_manual/chapter_4/ch4partsofurl.png" alt=""><figcaption></figcaption></figure>

* An API receives and processes web requests and returns response data to the requester. Any API request must end up with a response; failing to respond for any reason will make this request invalid.
* Different operations can be executed through APIs. For example, users can:
  * Save data to and retrieve it from Entities,
  * Send data to and receive data from connected sources,
  * Combine and transform data from multiple sources and return everything as a single response.
* API documentation is automatically generated. Users can share documentation internally or make it publicly available on the Internet.
* An API can be used in multiple API gateways; however, one API gateway can use only one API at a time.