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

# IB20Factory.isB20

> Returns whether an address matches the B20 address prefix, recovered from the address itself without consulting a registry.

## Signature

```solidity IB20Factory.sol theme={null}
function isB20(address token) external view returns (bool);
```

| Field               | Value            |
| ------------------- | ---------------- |
| Selector            | `0xfa19b927`     |
| Canonical signature | `isB20(address)` |

## Description

Returns `true` when `token` bears the `0xB2` address prefix (byte `[0]` is `0xB2`, bytes `[1:9]` are zero). The check reads the address directly; it does not consult a registry or any on-chain state. Never reverts.

<Note>
  `isB20` is a prefix-only check. It can return `true` for an address the Factory has not yet created. Use `isB20Initialized` when you need to confirm the token is live, that stronger check also requires the `0xef` bytecode stub the Factory plants during `createB20`.
</Note>

## Parameters

| Name    | Type      | Description       |
| ------- | --------- | ----------------- |
| `token` | `address` | Address to check. |

## Returns

| Type   | Description                                                          |
| ------ | -------------------------------------------------------------------- |
| `bool` | `true` if `token` matches the B20 address prefix; `false` otherwise. |

## Access Control

View, no access restriction.

## Policy Interaction

No policy interaction.

## Example

```solidity Usage Example theme={null}
IB20Factory(factory).isB20(token);
```