> ## 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. # Customize > Tailor DeepL translations to your domain with glossaries, style rules, custom instructions, and translation memories. DeepL's customization features let you control terminology, style, and consistency across your translations. ## What each feature does | Feature | What it controls | How it's applied | | :------------------------------------------------------------------------ | :----------------------------------------------------------------------------------- | :--------------------------------------------------------------------------- | | [Glossaries](/docs/customize/managing-glossaries) | Exact translations for specific terms, like product names or industry vocabulary | Stored on your account; passed per request via `glossary_id` | | [Style rules](/docs/customize/using-style-rules) | Formatting conventions (dates, numbers, punctuation) plus stored custom instructions | Stored on your account; passed per request via `style_id` | | [Custom instructions](/docs/customize/custom-instructions) | Tone, phrasing, and domain-specific behavior via natural-language directives | Inline per request via `custom_instructions`, or stored in a style rule list | | [Translation memories](/docs/customize/using-translation-memories) | Reuse of your previously approved translations for matching segments | Stored on your account; passed per request via `translation_memory_id` | | [Spoken terms](/docs/customize/improving-transcription-with-spoken-terms) | Recognition of specific terms during Voice API speech transcription | Stored on your account; passed per voice session via `spoken_terms_id` | Glossaries, style rules, custom instructions, and translation memories work with both [text translation](/docs/translate/translate-text-quickstart) and [document translation](/docs/translate/translate-documents-quickstart), support all `model_type` values, and can be combined in a single request. Spoken terms apply to [Voice API](/docs/voice/overview) sessions, where they can be combined with glossaries. Glossaries and style rules are unique to each of DeepL's global data centers and are not shared between them. Clients using [regional endpoints](/docs/getting-started/regional-endpoints) can't access glossaries or style rules created in the UI at this time. ## Choosing the right feature Here's when to use each customization feature for the best results. The [`context` parameter](/docs/learning-how-tos/examples-and-guides/how-to-use-context-parameter) can also be used to improve translations of ambiguous or short text. | Use case | Glossaries | Style rules | Custom instructions | Translation memories | Context parameter | | :------------------------------------------------------- | :--------: | :---------: | :-----------------: | :------------------: | :---------------: | | **Consistent domain-specific terminology** | ✅ | ❌ | ❌ | ❌ | ❌ | | **Brand and product names** | ✅ | ❌ | ❌ | ❌ | ❌ | | **Formatting conventions (dates, numbers, punctuation)** | ❌ | ✅ | ❌ | ❌ | ❌ | | **Tone and phrasing** | ❌ | ❌ | ✅ | ❌ | ❌ | | **Reusing previously approved translations** | ❌ | ❌ | ❌ | ✅ | ❌ | | **Ambiguous words or short snippets** | ❌ | ❌ | ❌ | ❌ | ✅ | | **Consistent gender or name spelling** | ❌ | ❌ | ❌ | ❌ | ✅ | ## Feature guides Create, edit, retrieve, and delete glossaries with the v3 endpoints, and use them in translations. Build style rule lists with configured rules and custom instructions, and apply them via style\_id. Best practices for writing natural-language instructions that produce consistent results. Retrieve your translation memories and control the matching threshold in translation requests. Keep company terms, acronyms, and names transcribed correctly in Voice API sessions. ## API reference Glossaries, style rules, and translation memories each have management endpoints under the [API Reference](/api-reference/multilingual-glossaries/create-a-glossary). If you're still on the deprecated v2 glossary endpoints, see [Glossary v2 vs v3 Endpoints](/docs/customize/glossary-v2-vs-v3-endpoints) for the differences and migration considerations.