> ## 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.

# Constants & addresses

> Copy B20 precompile addresses, roles, policy scopes, variant bytes, policy IDs, and supply-cap constants.

Use `StdPrecompiles.sol` and `B20Constants.sol` from `base-std` as the canonical Solidity source. This page lists the same values for quick reference.

## Precompile addresses

These addresses are identical on every network where B20 is active.

| Surface            | Address                                      |
| ------------------ | -------------------------------------------- |
| B20 Factory        | `0xB20f000000000000000000000000000000000000` |
| ActivationRegistry | `0x8453000000000000000000000000000000000001` |
| PolicyRegistry     | `0x8453000000000000000000000000000000000002` |

## Roles

| Role                    | Solidity constant                |
| ----------------------- | -------------------------------- |
| Default admin           | `bytes32(0)`                     |
| Mint                    | `keccak256("MINT_ROLE")`         |
| Burn                    | `keccak256("BURN_ROLE")`         |
| Deprecated blocked burn | `keccak256("BURN_BLOCKED_ROLE")` |
| Seize                   | `keccak256("SEIZE_ROLE")`        |
| Pause                   | `keccak256("PAUSE_ROLE")`        |
| Unpause                 | `keccak256("UNPAUSE_ROLE")`      |
| Metadata                | `keccak256("METADATA_ROLE")`     |
| Asset operator          | `keccak256("OPERATOR_ROLE")`     |

## Policy scopes

| Scope             | Solidity constant                       |
| ----------------- | --------------------------------------- |
| Transfer sender   | `keccak256("TRANSFER_SENDER_POLICY")`   |
| Transfer receiver | `keccak256("TRANSFER_RECEIVER_POLICY")` |
| Transfer executor | `keccak256("TRANSFER_EXECUTOR_POLICY")` |
| Mint receiver     | `keccak256("MINT_RECEIVER_POLICY")`     |
| Seize holder      | `keccak256("SEIZE_HOLDER_POLICY")`      |

## Policy IDs

| Name           | Value                                                                    |
| -------------- | ------------------------------------------------------------------------ |
| `ALWAYS_ALLOW` | `0`                                                                      |
| `ALWAYS_BLOCK` | `(uint64(uint8(IPolicyRegistry.PolicyType.ALLOWLIST)) << 56) \| 1` |

Custom policy IDs use this layout:

```text theme={null}
[8-bit PolicyType][56-bit counter]
```

Policy type bytes:

| PolicyType  |   Byte |
| ----------- | -----: |
| `BLOCKLIST` | `0x00` |
| `ALLOWLIST` | `0x01` |
| `UNION`     | `0x02` |
| `INTERSECT` | `0x03` |

## Variant bytes

| Variant      |   Byte | Address shape |
| ------------ | -----: | ------------- |
| `ASSET`      | `0x00` | `0xB200...`   |
| `STABLECOIN` | `0x01` | `0xB201...`   |

## Supply and decimals

| Constant                             |               Value |      |      |          |
| ------------------------------------ | ------------------: | ---- | ---- | -------- |
| Minimum Asset decimals               |                 `6` |      |      |          |
| Maximum Asset decimals               |                `18` |      |      |          |
| Maximum supply cap / no-cap sentinel | `type(uint128).max` |      |      |          |
| All features paused bitmask          |    `15` (\`TRANSFER | MINT | BURN | SEIZE\`) |

## Imports

```solidity theme={null}
import {StdPrecompiles} from "base-std/StdPrecompiles.sol";
import {B20Constants} from "base-std/lib/B20Constants.sol";
```

<CardGroup cols={2}>
  <Card title="Working with base-std" href="/base-chain/specs/upgrades/beryl/b20/specification/implementation/working-with-base-std" />

  <Card title="Policies & scopes" href="/base-chain/specs/upgrades/beryl/b20/specification/concepts/policies-and-scopes" />
</CardGroup>