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.
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
Pro API -> https://api.deepl.com

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Authentication

You need an authentication key to access the API. You can find your key in the “API Keys” tab in your account. 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)
Keep your API key secure at all times. Do not use it in client-side code.
If your authentication key becomes compromised, you also deactivate it and create a new key in the “API Keys” tab. Learn more about managing your DeepL API keys here. The authentication key is provided by setting the Authorization HTTP header to DeepL-Auth-Key [yourAuthKey].

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API Versions

The current API version is v2, meaning that all request paths start with /v2/. It is the only supported version, with the exception of CAT tool integrations, which need to use the version 1 API that is not documented here. If you intend to integrate DeepL Pro into a CAT tool or another tool assisting translation, please contact cat-tool.support@DeepL.com.