> ## Documentation Index
> Fetch the complete documentation index at: https://base-a060aa97-docs-add-b20-spec.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# IB20Factory.isB20

> Generated B20 reference for isB20(address).

[Related concept](/base-chain/specs/upgrades/beryl/b20/specification/implementation/deployment-and-initcalls-encoding)

## Signature

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

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

## Description

Returns whether `token` was created by this factory, recovered from the address prefix. Never reverts.
Param: token Address to check.
Return: Whether `token` matches the B-20 address prefix.

## Access control

Read-only or ERC-20-standard access rules unless the NatSpec states otherwise.

## Policy interaction

No direct policy interaction.

## Example

```solidity theme={null}
IB20Factory(target).isB20(arg0);
```

## Related

* [IB20Factory reference](/base-chain/specs/upgrades/beryl/b20/specification/reference/interfaces/IB20Factory)
* [Constants & addresses](/base-chain/specs/upgrades/beryl/b20/specification/reference/constants-and-addresses)