> ## Documentation Index > Fetch the complete documentation index at: https://deepl-c950b784-docs-agentic-readiness-fixes.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Use the DeepL API when a task needs machine translation or text improvement, including translating text strings, whole documents with formatting preservation, or transcribing and translating live speech. Preferred terminology and phrasing may be enforced using customizations (glossaries, style rules, and translation memories). Retrieve supported languages for each product from the `/v3/languages` endpoints. > Read the machine-readable API surface instead of inferring request shapes from prose: the REST spec is at https://developers.deepl.com/api-reference/openapi.yaml (also served as openapi.json) and the Voice WebSocket protocol is at https://developers.deepl.com/api-reference/voice/voice.asyncapi.yaml. These docs also expose an MCP server at https://developers.deepl.com/mcp (Streamable HTTP, no authentication). > Use https://api.deepl.com for Pro plans and https://api-free.deepl.com for the Free plan. Authenticate every request with the header `Authorization: DeepL-Auth-Key `. Never fabricate an API key: ask the user for one, or point them at https://developers.deepl.com/docs/getting-started/quickstart. > Errors use standard HTTP status codes with a JSON body containing a `message` field, plus a `code` field where available, and an `X-Trace-ID` response header that identifies the request in DeepL's logs. Log `X-Trace-ID` by default. Retry 429 and 5xx with exponential backoff. Do not retry 456, which means the account quota is exhausted, or 400, which means the request itself is invalid. # Alpha and beta features > Learn more about alpha and beta features in the DeepL API and how to best make use of them. You might see API features in the documentation that are labeled as "alpha" or "beta". You can find the official definition in our terms and conditions ([section 3.1.5](https://www.deepl.com/en/pro-license)): > 3.1.5 DeepL is free to provide customers with additional functions in alpha or beta versions on a test basis ("Test Functions"). These Test Functions are marked as such or as alpha or beta. Test Functions are not the subject of this Agreement. DeepL may make them available voluntarily to all or individual customers and the Customer is not obliged to make any payment for the use of Test Functions. Test Functions are intended for test use by the Customer and evaluation by DeepL. They are not final products or features and may contain bugs or other inaccuracies. DeepL can change, adapt or discontinue the Test Functions at any time. In summary, features labeled as alpha or beta: * Are not intended to be used in production * Could be deprecated by DeepL at any time and without advance notice * Could be changed in a way that breaks API clients relying on them at any time and without advance notice Please keep this in mind when exploring or testing features labeled as alpha or beta.