> ## 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 <api-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.

# Pre-production checklist

> Here's what we recommend reviewing to get your DeepL API application ready for production.

As you prepare to open your DeepL-powered application up to the world, these tips will help you get ready for production.

1. **Error handling:** If you receive 429 or 500 errors, use retries with exponential backoff. If you use one of [DeepL's official client libraries](/docs/getting-started/client-libraries), you get this functionality out-of-the-box.
2. **Persistent HTTP connection:** Especially for use cases with low latency requirements, we recommend using a persistent HTTP connection. [DeepL's official client libraries](/docs/getting-started/client-libraries) use [Keep-Alive](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Keep-Alive) by default.
3. **Use the correct content type:** For text translation (the `/translate` endpoint), use form-encoded (`Content-Type: application/x-www-form-urlencoded`) or JSON-encoded (`Content-Type: application/json`) request bodies.
   * Uploading a file for document translation requires an HTTP POST request with `Content-Type: multipart/form-data`; this content type should not be used for text translation.
4. **No query parameters:** Please do not make API requests using query parameters. The examples throughout the API reference include properly formed HTTP POST requests. For security reasons, be especially sure not to send your authentication key via query parameters.
5. **CORS requests:** It's not possible to send requests to the DeepL API from the browser, as requests to third-party APIs from front-end applications would expose your credentials on the web. [You can learn more here](/docs/best-practices/cors-requests).
6. **Translation context:** DeepL considers the broader context of a source text or document when translating. In general, including more context in a source text or document can result in a higher-quality DeepL translation. For text translation, you can also try the [`context` parameter](/api-reference/translate/request-translation). [Learn more about working with context here](/docs/learning-how-tos/examples-and-guides/how-to-use-context-parameter).
7. **Cache results from translation requests:** Storing API responses lets apps serve content faster and avoids extra costs from repeated requests for unchanged content.