> ## 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. # About > Understand what the DeepL API does. Animated DeepL banner The DeepL API provides programmatic access to DeepL’s language AI technology, making it possible to bring high quality translation capabilities directly to your websites and applications. ## Common use cases for the DeepL API: * **Website translation**: Localize websites and expand to new markets efficiently and at scale—even in sectors like e-commerce and news media with a large catalog of dynamic content. * **Company communications**: Integrate DeepL’s translation technology into your company’s systems such as Confluence and SharePoint. Enable your global teams to communicate seamlessly and with [maximum data security](https://www.deepl.com/pro-data-security/). * **Building multilingual products**: Translate chat conversations to connect users across language barriers in real time. Localize comments and product reviews with the click of a button. Make translation one of your differentiating features—however you imagine it. In addition, many leading computer-assisted translation (CAT) tool providers have [integrated DeepL’s technology into their software](https://support.deepl.com/hc/articles/360019358599-CAT-tools-supported). This lets translators benefit from DeepL’s high-quality neural translations within their favorite translation tool. If you would like to develop a DeepL plugin for your CAT tool, [please contact us at here](https://support.deepl.com/hc/en-us/requests/new). ## Why the DeepL API? * **High-quality text and document translations**: DeepL [consistently outperforms the competition](https://www.deepl.com/quality.html) in translation quality—and not only for text translation. The API also supports [many document, publishing, and localization formats](/api-reference/document/upload-and-translate-a-document) including DOCX, PPTX, XLSX, PDF, HTML, IDML, XLIFF, XML, JSON, DITA, and MIF. * **Maximum data security**: With DeepL API paid plans, texts aren’t saved on persistent storage and aren’t used to train our models. And DeepL adheres strictly to EU data protection laws and ISO 27001. [Learn more about data security at DeepL](https://www.deepl.com/pro-data-security/). * **Customization with glossaries**: [Specify your own translations for words and phrases](/docs/customize/managing-glossaries), and customize your translations consistently and at scale. To access the DeepL API, [sign up for a plan](https://www.deepl.com/en/pro#api).