Custom vocabularies - Amazon Transcribe

Custom vocabularies

Use custom vocabularies to improve transcription accuracy for one or more specific words. These are generally domain-specific terms, such as brand names and acronyms, proper nouns, and words that Amazon Transcribe isn't rendering correctly.

Custom vocabularies can be used with all supported languages. Note that only the characters listed in your language's character set can be used in a custom vocabulary.


You are responsible for the integrity of your own data when you use Amazon Transcribe. Do not enter confidential information, personal information (PII), or protected health information (PHI) into a custom vocabulary.

Considerations when creating a custom vocabulary:

  • You can have up to 100 custom vocabulary files per AWS account

  • The size limit for each custom vocabulary file is 50 Kb

  • If using the API to create your custom vocabulary, your vocabulary file must be in text (*.txt) format. If using the AWS Management Console, your vocabulary file can be in text (*.txt) format or comma-separated value (*.csv) format.

  • Each entry within a custom vocabulary cannot exceed 256 characters

  • To use a custom vocabulary, it must have been created in the same AWS Region as your transcription.


You can test your custom vocabulary using the AWS Management Console. Once your custom vocabulary is ready to use, log in to the AWS Management Console, select Real-time transcription, scroll to Customizations, toggle on Custom vocabulary, and select your custom vocabulary from the dropdown list. Then select start streaming. Speak some of the words in your custom vocabulary into your microphone to see if they render correctly.

Custom vocabulary tables versus lists


Custom vocabularies in list format are being deprecated. If you're creating a new custom vocabulary, use the table format.

Tables give you more options for—and more control over—the input and output of words within your custom vocabulary. With tables, you must specify multiple categories (Phrase and DisplayAs), allowing you to fine-tune your output.

Lists don't have additional options, so you can only type in entries as you want them to appear in your transcript, replacing all spaces with hyphens.

The AWS Management Console, AWS CLI, and AWS SDKs all use custom vocabulary tables in the same way; lists are used differently for each method and thus may require additional formatting for successful use between methods.

For more information, see Creating a custom vocabulary using a table and Creating a custom vocabulary using a list.

To dive a little deeper and learn how to use Amazon Augmented AI with custom vocabularies, see:

API operations specific to custom vocabularies