> ## Documentation Index
> Fetch the complete documentation index at: https://docs.belio.co.ke/llms.txt
> Use this file to discover all available pages before exploring further.

# Template Parameters

Template parameters supply the values for placeholders in the template content. Every parameter is a JSON object with exactly two fields and has no `type` discriminator on SMS parameters (unlike WhatsApp template parameters):

| Field   | Description                                                                       |
| ------- | --------------------------------------------------------------------------------- |
| `name`  | Placeholder name that must match a `{{name}}` placeholder in the template content |
| `value` | Substitution value inserted into the template                                     |

```json theme={null}
{ "name": "code", "value": "654321" }
```

## Placeholders

Template content uses double-brace placeholders, which can be **named** (`{{sample}}`, `{{code}}`) or **positional** (`{{1}}`, `{{2}}`). In a request, supply a parameter whose `name` matches the placeholder identifier. For a positional placeholder `{{1}}`, use `"name": "1"`. At send time the API replaces each placeholder with the corresponding parameter value, or with the parameter definition's default when one is omitted.

## Parameter definitions

Each template carries parameter definitions that govern validation. These are configured when the template is created:

```json theme={null}
{
  "name": "code",
  "format": "Numeric",
  "required": true,
  "maxLength": 6,
  "default": "123456"
}
```

| Field       | Type    | Default       | Description                                                       |
| ----------- | ------- | ------------- | ----------------------------------------------------------------- |
| `name`      | string  | —             | Parameter name; must match a placeholder in template content      |
| `format`    | string  | `"PlainText"` | Value format constraint                                           |
| `required`  | boolean | `true`        | Whether the client must supply the parameter                      |
| `maxLength` | integer | —             | Maximum allowed length of the value (optional)                    |
| `default`   | string  | —             | Default value used when the client omits the parameter (optional) |

## Parameter formats

The `format` on a parameter definition restricts what characters are allowed in the value:

| Format         | Allowed values                                                   | Typical use                                 |
| -------------- | ---------------------------------------------------------------- | ------------------------------------------- |
| `PlainText`    | Printable characters, except `{`, `}`, and control characters    | General short text (product names)          |
| `Alphanumeric` | Letters and digits only (A–Z, a–z, 0–9)                          | Reference codes, tokens without punctuation |
| `Numeric`      | Digits only (0–9)                                                | OTPs, PINs, numeric identifiers             |
| `Name`         | Unicode letters, spaces, hyphens, apostrophes (`^[\p{L}\s'-]+$`) | First names, surnames, display names        |

## Required vs optional parameters

For each placeholder in the template content:

* If you **provide** the parameter in `params`, it is validated against the definition.
* If you **omit** it and the definition has a `default`, the default is used automatically.
* If you **omit** it and there is no `default`, the request is rejected with `Missing required parameter '{name}'`.