> ## Documentation Index
> Fetch the complete documentation index at: https://deepl-c950b784-docs-style-rules-tm-language-expansion.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Access and authentication

> Learn where to find your authentication key and how to access the DeepL API.

The DeepL API is accessible through an HTTP interface as well as a selection of programming language-specific client libraries.

The API endpoints accept both form-encoded (`Content-Type: application/x-www-form-urlencoded`) and JSON-encoded (`Content-Type: application/json`) request bodies, and return JSON-encoded responses.

One exception regarding content type is the `/document` endpoint when uploading a document. Because this includes a file upload, it must be an HTTP POST request with content type `multipart/form-data`. Content type `multipart/form-data` should not be used with other endpoints such as `/translate`. It is only officially supported when used to upload a document via the `/document` endpoint.

There is a header size limit of 16 KiB (16\*1024 bytes) for all requests.

<Info>
  Please note: the API endpoint is different for the Free API and Pro API. You may have to adapt your code when using the code samples provided here!

  Free API -> `https://api-free.deepl.com` <br />
  Pro API -> `https://api.deepl.com`
</Info>

### Authentication

You need an authentication key to access the API. You can find your key in the ["API Keys" tab in your account](https://www.deepl.com/your-account/keys). It is important to keep your keys confidential. You should not use an API key in publicly-distributed code.

DeepL API Free authentication keys can be identified easily by the suffix ":fx" (e.g., 279a2e9d-83b3-c416-7e2d-f721593e42a0:fx)

<Info>
  Keep your API key secure at all times. Do not use it in client-side code.
</Info>

If your authentication key becomes compromised, you also deactivate it and create a new key in [the "API Keys" tab](https://www.deepl.com/your-account/keys).

Learn more about managing your DeepL API keys [here](/docs/getting-started/managing-api-keys).

The authentication key is provided by setting the *Authorization* HTTP header to `DeepL-Auth-Key [yourAuthKey]`.

#### API Versions

The primary API version is v2, meaning that most request paths start with `/v2/`. Some endpoints are also available under `/v3/` — see [v2 vs v3 glossary endpoints](/api-reference/glossaries/v2-vs-v3-endpoints) for details.

The previous version of the API (`/v1/`) is also available for compatibility reasons and matches v2 functionality. Usage is reported and billed normally when accessing v1 endpoints.

If you intend to integrate DeepL Pro into a CAT tool or another tool assisting translation, please contact [cat-tool.support@DeepL.com](mailto:cat-tool.support@DeepL.com).