# Inbound Caller ID Reformatting Rule Parameters

Inbound caller ID reformatting rules rewrite the number shown on an incoming call before it reaches your extensions, so you can drop unwanted leading digits or add a prefix of your own. When you export these rules, or build a CSV to import them in bulk, each row is one rule described by the columns below. Use this reference to complete every column correctly.

## Field reference

| Column | What it does | Required | Accepted values | Default |
| --- | --- | --- | --- | --- |
| Patterns | Defines the caller IDs the rule applies to. Any inbound caller ID that matches the pattern is reformatted according to the other columns. | Yes | Digits, letters, and the characters `[` `]` `*` `#` `(` `)` `.` `-` `+` `!`. Up to 31 characters. | N/A |
| Strip | The number of digits to remove from the start of the matched caller ID. | No | Digits only. Up to 2 characters. | N/A |
| Prepend | The digits to add to the front of the caller ID, applied after any stripping. | No | Digits, letters, and the characters `(` `)` `.` `-` `+` `*` `#`. Up to 31 characters. | N/A |

:::note
`Strip` and `Prepend` are optional, but a rule that leaves both empty makes no change to the caller ID. Set at least one of them for the rule to have an effect.
:::

:::tip
`Strip` runs first, then `Prepend` is added to what remains. Two examples:

- To show incoming numbers in E.164 format, leave `Strip` blank and set `Prepend` to `+`. A caller ID delivered as `12125550100` is displayed as `+12125550100`.
- To drop a leading digit your carrier adds (for example a `9`), set `Strip` to `1`. A caller ID of `92125550100` becomes `2125550100`.
:::