> ## 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.

# Breaking changes (Change Notices)

In this section, we'll outline **planned deprecations and breaking changes** that might affect applications using the DeepL API.

To learn about new releases, please see the [Release notes](/docs/resources/release-notes) page.

<Card title="July 2024: Deprecation of insecure cipher suites" href="/docs/resources/breaking-changes-change-notices/july-2024-deprecation-of-insecure-cipher-suites" />

<Card title="March 2025: Deprecating GET requests to /translate and authenticating with auth_key" href="/docs/resources/breaking-changes-change-notices/march-2025-deprecating-get-requests-to-translate-and-authenticating-with-auth_key" />

<Card title="November 2025: Deprecating query parameter and request body authentication" href="/docs/resources/breaking-changes-change-notices/november-2025-deprecation-of-legacy-auth-methods" />