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Style rules apply a reusable set of formatting and style conventions to your translations. A style rule list combines two types of rules:
  • Configured rules: predefined options for formatting conventions, like time format, number formatting, and punctuation
  • Custom instructions: your own natural-language instructions for requirements the predefined rules don’t cover
Both are applied together during translation. You can build style rule lists in the UI at deepl.com/custom-rules or manage them programmatically with the style rules endpoints, as shown below.
The Style Rules API is currently available only to Pro API subscribers.

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Create a style rule list

Send POST /v3/style_rules a name, the target language the rules apply to, and the rules themselves:
Example request
curl -X POST https://api.deepl.com/v3/style_rules \
  --header "Authorization: DeepL-Auth-Key $API_KEY" \
  --header "Content-Type: application/json" \
  --data '{
    "name": "Technical Documentation Rules",
    "language": "en",
    "configured_rules": {
      "dates_and_times": {
        "calendar_era": "use_bc_and_ad"
      },
      "punctuation": {
        "periods_in_academic_degrees": "do_not_use"
      }
    },
    "custom_instructions": [
      {
        "label": "Tone instruction",
        "prompt": "Use a friendly, diplomatic tone",
        "source_language": "en"
      }
    ]
}'
Example response
{
  "style_id": "a74d88fb-ed2a-4943-a664-a4512398b994",
  "name": "Technical Documentation Rules",
  "creation_time": "2024-10-01T12:34:56Z",
  "updated_time": "2024-10-01T12:34:56Z",
  "language": "en",
  "version": 1,
  "configured_rules": {
    "dates_and_times": {
      "calendar_era": "use_bc_and_ad"
    },
    "punctuation": {
      "periods_in_academic_degrees": "do_not_use"
    }
  },
  "custom_instructions": [
    {
      "id": "68fdb803-c013-4e67-b62e-1aad0ab519cd",
      "label": "Tone instruction",
      "prompt": "Use a friendly, diplomatic tone",
      "source_language": "en"
    }
  ]
}
The version field increments each time the list is modified, so you can track changes to your style rules. See the endpoint reference for all available configured rule categories and options, and the custom instructions guide for how to write instructions that work well.

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Apply style rules to a translation

Pass the list’s style_id in a /v2/translate or /v2/document request. The target language of the request has to match the style rule list’s language:
Example request
curl -X POST https://api.deepl.com/v2/translate \
  --header "Authorization: DeepL-Auth-Key $API_KEY" \
  --header "Content-Type: application/json" \
  --data '{
    "text": ["Das Treffen ist um 15:00 Uhr"],
    "source_lang": "DE",
    "target_lang": "EN",
    "style_id": "a74d88fb-ed2a-4943-a664-a4512398b994"
}'
All model_type values are supported with style rules. Style rules apply to root languages, so a list with language: "en" works for EN-US and EN-GB targets alike; see How to Apply Customizations to Language Variants.

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Update a style rule list

As with glossaries, the update methods have different scopes: Custom instructions are managed individually within a list: To list or inspect rule lists, use GET /v3/style_rules (add detailed=true to include each list’s rules and instructions) or GET /v3/style_rules/{style_id}. Deleting a list with DELETE /v3/style_rules/{style_id} cannot be undone.

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Limits

  • Style rule lists support target languages de, en, es, fr, it, ja, ko, and zh
  • There is no limit on the number of configured rules per list
  • A list can hold up to 200 custom instructions (this cap may be adjusted per plan tier in the future); each instruction prompt is limited to 300 characters
  • If you need more than 200 custom instructions, split your rules across multiple style rule lists for different content types