# Patterns

Patterns help recover short, structured alphanumeric tokens - order codes, reference numbers, licence plates - that are easy to mishear when spoken letter-by-letter and digit-by-digit. When you know the shape of a token that may appear in the audio, describe it with a subset of regular-expression syntax and the transcription is corrected to fit.

Patterns are available on the [Prerecorded](/speech-to-text/prerecorded/), [Realtime](/speech-to-text/realtime/), and [Turns](/speech-to-text/turns/) APIs.

## Using Patterns

Pass the `patterns` query parameter as a comma-separated list of patterns. Each one describes a single token to recover.

```
?patterns=AMZ[0-9]{6}
?patterns=[A-Z]{2}[0-9]{2} [A-Z]{3}
?patterns=(INV)?[0-9]{4,5}
?patterns=AMZ[0-9]{6},ORD[0-9]{5}
```

Patterns use a subset of regular-expression syntax:

| Syntax     | Meaning                                      | Example             |
|------------|----------------------------------------------|---------------------|
| `[0-9]`    | a digit                                      | `[0-9]{6}`          |
| `[A-Z]`    | a letter                                     | `[A-Z]{3}`          |
| `{n}`      | repeat the preceding class exactly `n` times | `[0-9]{6}`          |
| `{m,n}`    | repeat the preceding class `m` to `n` times  | `[0-9]{4,6}`        |
| `(...)?`   | an optional group - matched only when spoken | `(INV)?[0-9]{5}`    |
| `AMZ`      | literal letters/digits, e.g. a fixed prefix  | `AMZ[0-9]{6}`       |
| ` ` or `-` | a separator                                  | `[A-Z]{2} [0-9]{3}` |

Optional groups and ranges are resolved against the audio: an optional prefix is added only when it is actually spoken, and a `{m,n}` range adopts the spoken length. The more specific the pattern, the better - a fixed prefix or known structure (`AMZ[0-9]{6}`) is recovered more reliably than an open one.

A pattern matches tokens of at most 32 characters once fully expanded (the prefix and any digits or letters combined); a longer range or repeat is clamped to this limit. This is well above the length of typical order codes and reference numbers.

## Examples

| Token type                | Example value           | Pattern                     |
|---------------------------|-------------------------|-----------------------------|
| Order code                | `AMZ374019`             | `AMZ[0-9]{6}`               |
| Reference number          | `4429105538`            | `[0-9]{10}`                 |
| Licence plate             | `RU77 TVG`              | `[A-Z]{2}[0-9]{2} [A-Z]{3}` |
| Invoice (optional prefix) | `INV4821` or `4821`     | `(INV)?[0-9]{4}`            |
| Variable-length code      | `AMZ3740` … `AMZ374019` | `AMZ[0-9]{4,6}`             |

:::caution[Only set patterns you expect]
Patterns improve accuracy on audio that contains the token, but can **degrade** transcription of audio that does not. Set `patterns` only when the expected token is likely present in the request - don't apply them globally.
:::

See the API reference for [Prerecorded](/api/speech-to-text/prerecorded/), [Realtime](/api/speech-to-text/realtime/), and [Turns](/api/speech-to-text/turns/).