ERC20 Precompile

Introduction

The ERC20 precompile provides a standard ERC20 token interface for interacting with assets managed by the Assets pallet, helping smart contracts to interact with native Polkadot assets (such as USDT, USDC, and other tokens) using familiar Ethereum-style ERC20 calls. Polkadot Hub runs three instances of the Assets pallet — Trust-Backed Assets, Foreign Assets, and Pool Assets — each mapped to a distinct ERC20 precompile address suffix.

Each asset is mapped to a unique precompile address based on its asset ID or foreign asset index. The precompile implements core ERC20 functionality:

• Token transfers: Send assets between accounts using standard transfer and transferFrom methods.
• Approvals and allowances: Manage spending permissions with approve and allowance.
• Balance queries: Check token balances with balanceOf and total supply with totalSupply.

Supported Asset Types

The ERC20 precompile supports three categories of assets, each with its own address suffix.

Trust-Backed Assets

Trust-Backed Assets are created directly in the Assets pallet on Polkadot Hub and assigned a u32 asset ID.

• Address suffix: 01200000
• Address format: 0x + assetId (8 hex digits, zero-padded) + 24 zero digits + 01200000
• Example: Asset ID 1984 → 0x000007C000000000000000000000000001200000

Foreign Assets

Foreign Assets originate from other chains and are identified on-chain by their XCM Location. The ERC20 precompile uses a u32 index—not the XCM Location directly—to derive the precompile address.

• Address suffix: 02200000
• Address format: 0x + foreignAssetIndex (8 hex digits, zero-padded) + 24 zero digits + 02200000
• Example: Foreign Asset Index 0 → 0x0000000000000000000000000000000002200000

Deriving the Foreign Asset Index

Since foreign asset IDs are XCM Locations (not simple integers), the runtime assigns each foreign asset a sequential u32 index when it is registered. To derive the ERC20 precompile address for a foreign asset, follow these steps:

1. Get the XCM location of the foreign asset (for example, { parents: 1, interior: X1(Parachain(2313)) }).

2. Query the index in Polkadot.js Apps:

   1. Navigate to Developer > Chain State.
   2. Select assetsPrecompiles from the module dropdown.
   3. Select foreignAssetIdToAssetIndex from the call dropdown.
   4. Pass the XCM Location and note the returned u32 value (for example, 5).

   

3. Enter that u32 index into the Foreign Asset mode of the converter above to derive the ERC20 precompile address.

Pool Assets

Pool Assets are created by liquidity pool operations on Polkadot Hub and assigned a u32 asset ID.

• Address suffix: 03200000
• Address format: 0x + assetId (8 hex digits, zero-padded) + 24 zero digits + 03200000
• Example: Pool Asset ID 0 → 0x0000000000000000000000000000000003200000

Precompile Interface

The ERC20 precompile implements a subset of the standard ERC20 interface. The following functions are available:

IERC20-precompile.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IERC20 {
    // Implemented functions
    function totalSupply() external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
}

Metadata Functions Not Available

The optional ERC20 metadata functions (name(), symbol(), decimals()) are not implemented in this precompile. These functions are only available through the Assets pallet's storage, not via the ERC20 interface.

Query Functions

Get Total Supply

Returns the total number of tokens in circulation for this asset.

function totalSupply() external view returns (uint256);

Returns:

• uint256: The total supply of tokens

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
uint256 supply = token.totalSupply();

Get Balance

Returns the token balance of a specific account address.

function balanceOf(address account) external view returns (uint256);

Parameters:

• account: The address to query

Returns:

• uint256: The token balance of the account

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
address user = 0x1234567890123456789012345678901234567890;
uint256 balance = token.balanceOf(user);

Check Allowance

Returns the amount of tokens that the spender is allowed to spend on behalf of the owner.

function allowance(address owner, address spender) external view returns (uint256);

Parameters:

• owner: The account that owns the tokens
• spender: The account authorized to spend

Returns:

• uint256: The remaining allowance

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
address owner = 0x1111111111111111111111111111111111111111;
address spender = 0x2222222222222222222222222222222222222222;
uint256 remaining = token.allowance(owner, spender);

Token Operations

Transfer Tokens

Transfers tokens from the caller's account to the recipient address.

function transfer(address to, uint256 amount) external returns (bool);

Parameters:

• to: The recipient address
• amount: The amount of tokens to transfer

Returns:

• bool: true if the transfer was successful

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
address recipient = 0x3333333333333333333333333333333333333333;
uint256 amount = 1000 * 10**10; // Assuming 10 decimals

bool success = token.transfer(recipient, amount);
require(success, "Transfer failed");

Warning

The transfer will fail if the caller doesn't have sufficient balance.

Approve Spending

Approves the spender to withdraw up to a specified amount from the caller's account.

function approve(address spender, uint256 amount) external returns (bool);

Parameters:

• spender: The address authorized to spend tokens
• amount: The maximum amount the spender can withdraw

Returns:

• bool: true if the approval was successful

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
address spender = 0x4444444444444444444444444444444444444444;
uint256 amount = 500 * 10**10;

bool success = token.approve(spender, amount);
require(success, "Approval failed");

Transfer From

Transfers tokens from one account to another using the allowance mechanism. The caller must have sufficient allowance from the from account.

function transferFrom(address from, address to, uint256 amount) external returns (bool);

Parameters:

• from: The account to transfer from
• to: The recipient address
• amount: The amount of tokens to transfer

Returns:

• bool: true if the transfer was successful

Example usage:

IERC20 token = IERC20(0x000007C000000000000000000000000001200000);
address owner = 0x5555555555555555555555555555555555555555;
address recipient = 0x6666666666666666666666666666666666666666;
uint256 amount = 250 * 10**10;

bool success = token.transferFrom(owner, recipient, amount);
require(success, "Transfer from failed");

For the complete implementation, refer to the ERC20 precompile source code in the Polkadot SDK.

Common Trust-Backed Asset IDs

The following well-known Trust-Backed Assets are registered on Polkadot Hub and accessible via the ERC20 precompile:

Asset ID	Symbol	Name	Decimals	ERC20 Precompile Address
1984	USDt	Tether USD	6	0x000007C000000000000000000000000001200000
1337	USDC	USD Coin	6	0x0000053900000000000000000000000001200000

Note

The on-chain symbol for Tether on Polkadot Hub is USDt, which is commonly referred to as "USDT" on exchanges and in wallets.

Interact with the ERC20 Precompile

To interact with the ERC20 precompile in Remix IDE:

1. Create a new file called IERC20-precompile.sol in Remix

2. Copy and paste the IERC20 interface code shown above into the file

   

3. Compile the interface by selecting the compile button or using Ctrl + S

4. Calculate the ERC20 precompile address for your asset using the converter above. Select the appropriate asset type (Trust-Backed, Foreign, or Pool), then enter the asset ID or foreign asset index.

   • Trust-Backed example: Asset ID 1984 (USDt) → 0x000007C000000000000000000000000001200000
   • Foreign Asset example: Foreign Asset Index 0 → 0x0000000000000000000000000000000002200000

5. In the Deploy & Run Transactions tab, select the IERC20 interface from the contract dropdown

6. Enter the calculated precompile address in the At Address input field

7. Select the At Address button to connect to the precompile

   

Once connected, you can interact with any of the ERC20 precompile functions directly through the Remix interface.

Conclusion

The ERC20 precompile provides seamless integration between Polkadot's native asset management and Ethereum's familiar token standard. By mapping asset IDs to deterministic precompile addresses, developers can interact with native Polkadot assets using standard ERC20 interfaces.

Whether you're building DeFi protocols, token swaps, or any application requiring asset interactions, the ERC20 precompile enables you to leverage Polkadot's rich asset ecosystem with the same tools and patterns used in Ethereum development.

Reference

• ERC20 precompile source code
• Assets pallet documentation
• EIP-20: Token Standard