B20 Native Token Standard - Base Documentation

B20 is the Base ecosystem’s own version of ERC-20. It ships with a built-in compliance toolkit: transfer policies, freeze-and-seize, role-based access control, memos, and supply caps. The full interface specs are available in the Base Standard Library repository. B20 tokens are implemented as Rust precompiles rather than EVM smart contracts, making them faster, cheaper, and more native to the chain. All tokens are deployed via the singleton B20Factory precompile. To deploy your first B20 token, see the Launch a B20 Token quickstart.

Verify the ActivationRegistry is enabled before attempting to deploy.

B20 supports two variants:

Variant	Decimals	Additional Features
Asset	6–18 (configurable)	Rebase multiplier, onchain announcements, batched issuance
Stablecoin	6 (fixed)	Self-declared fiat currency code

ERC-20 compatibility

B20 is a superset of ERC-20. Every ERC-20 call (transfer, transferFrom, approve, balanceOf, allowance, and the standard events) behaves exactly as the standard specifies, so existing ERC-20 tooling and integrations work against B20 with no changes.

B20 adds methods that ERC-20 does not include: memos, mint/burn, policy gating, granular pause, and ERC-2612 permit. These extend ERC-20 without altering it - every ERC-20 method exists on B20, but the reverse does not hold. For the complete ABIs, see the interface definitions in the Base Standard Library.

Roles model

B20 role-based access control extends OpenZeppelin AccessControl with a fixed set of roles and one behavioral override on admin renunciation.

Role	Gates
`DEFAULT_ADMIN_ROLE`	All admin operations: role grants, policy updates, supply-cap changes
`MINT_ROLE`	`mint`, `mintWithMemo`
`BURN_ROLE`	Caller-side burns: `burn`, `burnWithMemo`
`BURN_BLOCKED_ROLE`	Third-party burns against policy-blocked accounts: `burnBlocked`
`PAUSE_ROLE`	`pause`
`UNPAUSE_ROLE`	`unpause`
`METADATA_ROLE`	`updateName`, `updateSymbol`, `updateContractURI`

User-defined roles are supported via setRoleAdmin and grantRole. They carry no built-in effect - B20 only enforces gates against the seven base-surface roles above. The Asset variant adds an eighth role, OPERATOR_ROLE (see Variants).

Run a token without an admin

The last DEFAULT_ADMIN_ROLE holder cannot be removed via renounceRole or revokeRole (both revert with LastAdminCannotRenounce). The dedicated renounceLastAdmin() is the only path to permanently transition a token to admin-less. Tokens that intend to launch admin-less from the start pass initialAdmin == address(0) at creation, which never grants the role and skips the renounceLastAdmin step entirely. After renounceLastAdmin() (or for tokens deployed with initialAdmin == address(0)):

Operations gated by DEFAULT_ADMIN_ROLE become permanently uncallable.
Roles already granted to other addresses (MINT_ROLE, BURN_ROLE, etc.) continue to function independently.
Admin resurrection is blocked: grantRole, revokeRole, and setRoleAdmin all revert with AccessControlUnauthorizedAccount even if the caller holds a custom role.

PolicyRegistry

The PolicyRegistry is a singleton precompile that manages allowlists and blocklists. B20 tokens reference policies by uint64 ID. Any caller can create a policy and nominate its admin.

State-changing functions on the PolicyRegistry are gated by the ActivationRegistry, which tracks which Base features are live. Read functions (isAuthorized, policyExists, policyAdmin, pendingPolicyAdmin) are always callable.

Policy types

Type	Default	Behavior
`BLOCKLIST`	Authorized	All accounts authorized by default; explicitly listed accounts are denied.
`ALLOWLIST`	Denied	All accounts denied by default; explicitly listed accounts are authorized.

Policy IDs

Policy IDs are uint64 values. The top byte encodes the PolicyType; the low 56 bits are a global counter starting at 2. Two built-in IDs require no creation:

Constant	ID	Behavior
`ALWAYS_ALLOW`	`0`	Authorizes every account unconditionally. Default scope value on new B20 tokens.
`ALWAYS_BLOCK`	`(uint64(ALLOWLIST) << 56) \| 1`	Denies every account unconditionally.

isAuthorized never reverts on a non-existent policy ID - it collapses to empty-member-set semantics (non-existent BLOCKLIST authorizes everyone; non-existent ALLOWLIST denies everyone).

Consumers that write a policy ID (e.g. updatePolicy) MUST validate policyExists(policyId) at write time to avoid silently binding to an unintended empty-set policy.

Policy admin

Each policy has one admin. Admin transfers are two-step: the current admin calls stageUpdateAdmin(policyId, newAdmin), then the pending admin calls finalizeUpdateAdmin(policyId). renounceAdmin(policyId) permanently freezes the policy - membership can never be changed again.

Create and manage policies

// Create a policy (admin first, then type)
uint64 policyId = policyRegistry.createPolicy(adminAddress, PolicyType.BLOCKLIST);
// Or seed the initial member set in one call:
// uint64 policyId = policyRegistry.createPolicyWithAccounts(adminAddress, PolicyType.BLOCKLIST, accounts);

// Update membership (batched). The setter is type-specific; the bool sets membership state.
policyRegistry.updateBlocklist(policyId, true, accounts);   // block these accounts
policyRegistry.updateBlocklist(policyId, false, accounts);  // unblock these accounts
// For ALLOWLIST policies: policyRegistry.updateAllowlist(policyId, allowed, accounts)

Read a policy from the PolicyRegistry

Method	Description
`isAuthorized(policyId, account)`	Whether `account` is authorized under `policyId`. Never reverts.
`policyExists(policyId)`	Whether a policy with this ID has been created.
`policyAdmin(policyId)`	Current admin address.
`pendingPolicyAdmin(policyId)`	Pending admin during a two-step transfer.

Token policy scopes

B20 declares a fixed set of policy scopes. Each scope stores a uint64 policy ID pointing into the PolicyRegistry. On every gated operation, B20 calls isAuthorized against the relevant scope and reverts with PolicyForbids if the account is not authorized.

Scope	Gates
`TRANSFER_SENDER_POLICY`	The `from` of `transfer` / `transferFrom`
`TRANSFER_RECEIVER_POLICY`	The `to` of `transfer` / `transferFrom`
`TRANSFER_EXECUTOR_POLICY`	The `msg.sender` of `transferFrom`, when distinct from `from` (not checked on `transfer`)
`MINT_RECEIVER_POLICY`	The `to` of `mint`

approve is not policy-gated - only actual balance movement via transfer / transferFrom is checked.

Every scope defaults to ALWAYS_ALLOW at token creation unless overridden in the bootstrap initCalls. An unattended B20 deployment is fully open - token behavior must be intentionally constrained.

Read a token’s policy assignments

Each B20 token exposes its scopes and their current policy IDs directly, so integrators can discover which policies apply without simulating a transfer.

Method	Description
`TRANSFER_SENDER_POLICY()`, `TRANSFER_RECEIVER_POLICY()`, `TRANSFER_EXECUTOR_POLICY()`, `MINT_RECEIVER_POLICY()`	The `bytes32` scope constants.
`policyId(scope)`	The `uint64` policy ID configured for `scope`. Returns `0` (`ALWAYS_ALLOW`) for a scope that has never been assigned. Reverts with `UnsupportedPolicyType` if the scope is not recognized.

To change an assignment, the token admin calls updatePolicy(scope, policyId), which emits PolicyUpdated and reverts if the scope is not recognized.

Check if a transfer will succeed

To confirm an account can move tokens, read each scope’s policy ID from the token and check it against the PolicyRegistry, then check pause state:

Read-only transferability check

// Will transferFrom(from, to, amount), executed by `executor`, pass policy and pause checks?
IPolicyRegistry registry = IPolicyRegistry(0x8453000000000000000000000000000000000002);

bool allowed =
    registry.isAuthorized(token.policyId(token.TRANSFER_SENDER_POLICY()), from) &&
    registry.isAuthorized(token.policyId(token.TRANSFER_RECEIVER_POLICY()), to) &&
    (executor == from || registry.isAuthorized(token.policyId(token.TRANSFER_EXECUTOR_POLICY()), executor)) &&
    !token.isPaused(PausableFeature.TRANSFER);

For a plain transfer, drop the executor check. Balance and allowance checks still apply as in ERC-20, and policy or pause state can change between the read and the transfer.

Token operations

The token surface beyond ERC-20: issuance, memos, pause, signed approvals, and metadata.

Mint

New supply is created via mint / mintWithMemo, gated by MINT_ROLE. The recipient is policy-checked against MINT_RECEIVER_POLICY. The operation reverts with SupplyCapExceeded if it would push totalSupply past the cap.

Burn

Two burn paths exist:

burn / burnWithMemo - caller burns from their own balance. Gated by BURN_ROLE.
burnBlocked - burns from a third party’s balance. Gated by BURN_BLOCKED_ROLE. The target account MUST be denied by TRANSFER_SENDER_POLICY - this is the freeze-and-seize path for regulated issuers.

Supply cap

The supply cap is optional. The sentinel type(uint128).max indicates no cap (the default at creation); it is also the maximum permitted cap, so totalSupply can never exceed it. updateSupplyCap(newCap) is admin-gated and emits SupplyCapUpdated. It reverts with InvalidSupplyCap if newCap is below the current totalSupply or above type(uint128).max.

Memos

A memo is an optional bytes32 payload attached to a token operation for offchain reference. Every memo-emitting operation emits Memo(address indexed caller, bytes32 indexed memo) immediately after the operation’s primary event. Indexers join via (transactionHash, logIndex − 1). Memo-emitting entrypoints: transferWithMemo, transferFromWithMemo, mintWithMemo, burnWithMemo.

Pause

Pauses are granular: the PausableFeature enum partitions the token surface into independently pausable operations - TRANSFER, MINT, and BURN. The enum is append-only. pause(features) and unpause(features) are gated by separate roles (PAUSE_ROLE and UNPAUSE_ROLE) by design. Pause state is publicly readable:

Method	Description
`isPaused(feature)`	Whether `feature` is currently paused. O(1).
`pausedFeatures()`	All currently paused features. Order is implementation-defined - treat the result as a set.

Pause changes emit Paused(address indexed updater, PausableFeature[] features) and Unpaused(address indexed updater, PausableFeature[] features).

Permit (ERC-2612)

B20 implements ERC-2612 (signed approvals) using an EIP-712 domain shaped as (name, version, chainId, verifyingContract), with version fixed at "1". updateName rotates the domain separator and emits EIP712DomainChanged (ERC-5267). ERC-1271 contract signatures are not accepted - ECDSA only.

Contract URI (ERC-7572)

contractURI() returns a string pointing to offchain metadata per ERC-7572. updateContractURI(newUri) is gated by METADATA_ROLE.

Update name and symbol

METADATA_ROLE gates:

updateName(newName) - updates name and rotates the EIP-712 domain separator. Emits NameUpdated and EIP712DomainChanged.
updateSymbol(newSymbol) - updates symbol only. Emits SymbolUpdated.

B20Factory

All B20 tokens are created through the singleton B20Factory precompile via createB20(variant, salt, params, initCalls). In base-std it is exposed as StdPrecompiles.B20_FACTORY.

Parameter	Description
`variant`	`ASSET` or `STABLECOIN`
`salt`	Caller-chosen entropy for address derivation
`params`	ABI-encoded, variant-specific creation struct (versioned by leading byte)
`initCalls`	Optional array of ABI-encoded calls dispatched post-creation; factory-originated calls bypass role gates and transfer-side policy gates during this window

createB20 reverts with IActivationRegistry.FeatureNotActivated if the requested variant’s feature is not yet activated on the chain.

Address derivation

B20 addresses are deterministic and encode the variant directly:

[10-byte B20 prefix][1-byte variant][9-byte keccak256(deployer, salt)]

The variant is recoverable from the address alone without an RPC call — inspect byte 10 (zero-indexed) to identify the token type. Helper functions getB20Address(variant, deployer, salt), isB20(addr), and isB20Initialized(addr) are available on the factory.

initCalls semantics

initCalls are dispatched after token creation. During this bootstrap window, factory-originated calls bypass the token’s role gates and its transfer-side policy gates (TRANSFER_SENDER_POLICY, TRANSFER_RECEIVER_POLICY, TRANSFER_EXECUTOR_POLICY), allowing admin-gated configuration (e.g. setting policies, granting roles) and bootstrap transfers in the same transaction as deployment. The bypass is deliberately not total:

MINT_RECEIVER_POLICY is always enforced even during initCalls.
Pause state is never bypassed.
Token invariants (supply cap, etc.) are never bypassed.

Variants

Each variant is identified by a 1-byte value encoded directly in the token’s address (see Address derivation):

Variant	Byte
`ASSET`	`0x00`
`STABLECOIN`	`0x01`

Asset

The general-purpose variant for assets of all kinds. Decimals are configurable between 6 and 18 at deployment time and are immutable after creation. In addition to the base B20 surface, Asset tokens add several capabilities. A new OPERATOR_ROLE gates the multiplier and announcements; batch mint and extra metadata reuse the existing MINT_ROLE and METADATA_ROLE respectively.

Multiplier

A WAD-precision rebase multiplier applied to all balance reads. Raw balances are stored unchanged; the multiplier scales the view returned to callers.

Method	Description
`multiplier()`	Current WAD-precision multiplier
`scaledBalanceOf(account)`	Raw balance × multiplier
`toScaledBalance(raw)`	Convert raw amount to scaled
`toRawBalance(scaled)`	Convert scaled amount to raw
`updateMultiplier(newMultiplier)`	Update the multiplier. Gated by `OPERATOR_ROLE`.

Announcements

Onchain disclosure brackets that wrap sensitive operations (e.g. batch mints, multiplier updates) with a public notice period. Gated by OPERATOR_ROLE. announce(internalCalls, id, description, uri) emits an Announcement event, executes internalCalls, then emits EndAnnouncement. The id must be unique and is enforced forever. Inner call reverts are wrapped in InternalCallFailed. internalCalls is executed but not emitted in either event (see Events for the full signatures). Apps that need the call payloads must read them from the transaction calldata.

Batch mint

batchMint(recipients, amounts) mints to multiple recipients in a single call. Gated by MINT_ROLE. Should be wrapped in announce() for transparency.

Extra metadata

An arbitrary key/value store for issuer-defined onchain metadata.

Method	Description
`extraMetadata(key)`	Read a value by key
`updateExtraMetadata(key, value)`	Write a value. Gated by `METADATA_ROLE`. Setting an empty value removes the entry.

Stablecoin

The fixed-decimals, fiat-backed carveout. Decimals are hard-wired to 6 and are not configurable. Adds currency(), which returns an ISO-style currency code string (e.g. "USD", "EUR"). The code is set once at creation via B20StablecoinCreateParams.currency, restricted to characters A-Z only. It is self-declared and not verified against any external registry.

Events

Full event interfaces, verbatim from the Base Standard Library. indexed parameters are the log topics apps can filter on.

All B20 token events

Every B20 token emits these, regardless of variant.

Event	Emitted by
`Transfer(address indexed from, address indexed to, uint256 amount)`	Transfers; `mint` (`from` = zero address) and `burn` (`to` = zero address)
`Approval(address indexed owner, address indexed spender, uint256 amount)`	`approve`, `permit`
`Memo(address indexed caller, bytes32 indexed memo)`	The `*WithMemo` entrypoints, after the operation’s primary event
`BurnedBlocked(address indexed caller, address indexed from, uint256 amount)`	`burnBlocked`
`RoleGranted(bytes32 indexed role, address indexed account, address indexed sender)`	`grantRole`
`RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender)`	`revokeRole`, `renounceRole`
`RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole)`	`setRoleAdmin`
`LastAdminRenounced(address indexed previousAdmin)`	`renounceLastAdmin`
`Paused(address indexed updater, PausableFeature[] features)`	`pause`
`Unpaused(address indexed updater, PausableFeature[] features)`	`unpause`
`PolicyUpdated(bytes32 indexed policyScope, uint64 oldPolicyId, uint64 newPolicyId)`	`updatePolicy`
`SupplyCapUpdated(address indexed updater, uint256 oldSupplyCap, uint256 newSupplyCap)`	`updateSupplyCap`
`ContractURIUpdated()`	`updateContractURI`
`NameUpdated(address indexed updater, string newName)`	`updateName`
`SymbolUpdated(address indexed updater, string newSymbol)`	`updateSymbol`
`EIP712DomainChanged()`	`updateName` (ERC-5267 domain rotation)

Asset variant events

Event	Emitted by
`MultiplierUpdated(uint256 multiplier)`	`updateMultiplier`
`ExtraMetadataUpdated(string key, string value)`	`updateExtraMetadata`
`Announcement(address indexed caller, string id, string description, string uri)`	`announce`, before the internal calls execute
`EndAnnouncement(string id)`	`announce`, after the internal calls execute

PolicyRegistry events

Event	Emitted by
`PolicyCreated(uint64 indexed policyId, address indexed creator, PolicyType policyType)`	`createPolicy`, `createPolicyWithAccounts`
`PolicyAdminStaged(uint64 indexed policyId, address indexed currentAdmin, address indexed pendingAdmin)`	`stageUpdateAdmin`
`PolicyAdminUpdated(uint64 indexed policyId, address indexed previousAdmin, address indexed newAdmin)`	`finalizeUpdateAdmin`, `renounceAdmin`
`AllowlistUpdated(uint64 indexed policyId, address indexed updater, bool allowed, address[] accounts)`	`updateAllowlist`
`BlocklistUpdated(uint64 indexed policyId, address indexed updater, bool blocked, address[] accounts)`	`updateBlocklist`

B20Factory events

Event	Emitted by
`B20Created(address indexed token, B20Variant indexed variant, string name, string symbol, uint8 decimals, bytes variantEventParams)`	`createB20`, after the token’s identity is sealed and before `initCalls` are dispatched

variantEventParams carries variant-specific immutable identity data, ABI-encoded and prefixed with a version byte: empty for ASSET; the currency code for STABLECOIN.

ActivationRegistry events

Event	Emitted by
`FeatureActivated(bytes32 indexed feature, address indexed caller)`	Feature activation
`FeatureDeactivated(bytes32 indexed feature, address indexed caller)`	Feature deactivation

Precompile addresses

These addresses are identical on every network where B20 is active (Mainnet, Base Sepolia, Vibenet, and local base-anvil).

Precompile	Address
B20Factory	`0xB20f000000000000000000000000000000000000`
ActivationRegistry	`0x8453000000000000000000000000000000000001`
PolicyRegistry	`0x8453000000000000000000000000000000000002`

​ERC-20 compatibility

​Roles model

​Run a token without an admin

​PolicyRegistry

​Policy types

​Policy IDs

​Policy admin

​Create and manage policies

​Read a policy from the PolicyRegistry

​Token policy scopes

​Read a token’s policy assignments

​Check if a transfer will succeed

​Token operations

​Mint

​Burn

​Supply cap

​Memos

​Pause

​Permit (ERC-2612)

​Contract URI (ERC-7572)

​Update name and symbol

​B20Factory

​Address derivation

​initCalls semantics

​Variants

​Asset

​Multiplier

​Announcements

​Batch mint

​Extra metadata

​Stablecoin

​Events

​All B20 token events

​Asset variant events

​PolicyRegistry events

​B20Factory events

​ActivationRegistry events

​Precompile addresses

ERC-20 compatibility

Roles model

Run a token without an admin

PolicyRegistry

Policy types

Policy IDs

Policy admin

Create and manage policies

Read a policy from the PolicyRegistry

Token policy scopes

Read a token’s policy assignments

Check if a transfer will succeed

Token operations

Mint

Burn

Supply cap

Memos

Pause

Permit (ERC-2612)

Contract URI (ERC-7572)

Update name and symbol

B20Factory

Address derivation

initCalls semantics

Variants

Asset

Multiplier

Announcements

Batch mint

Extra metadata

Stablecoin

Events

All B20 token events

Asset variant events

PolicyRegistry events

B20Factory events

ActivationRegistry events

Precompile addresses