Skip to main content
Tempo’s fee system enables users to pay transaction fees in any USD-denominated TIP-20 stablecoin. The protocol automatically converts between different stablecoins using the Fee AMM, ensuring validators receive fees in their preferred token while users pay in theirs.

​
Key Features

​
Stablecoin Gas Payments

Unlike traditional blockchains that require native tokens for gas, Tempo accepts any USD-denominated TIP-20 token as a fee payment method. Users can pay fees in:
  • pathUSD (0x20C0000000000000000000000000000000000000) - Tempo’s native stablecoin
  • USDC, USDT, or any other USD-denominated TIP-20 token
  • Any token the validator accepts (determined by Fee AMM liquidity)
This eliminates the need to acquire and manage a separate gas token, simplifying the user experience for payment applications.

​
Target Cost Model

Tempo’s gas pricing targets predictable dollar costs for common operations:
OperationTarget CostGas Amount
TIP-20 transfer (existing address)$0.0001 (0.1 cents)50,000 gas
TIP-20 transfer (new address)$0.0006 (0.6 cents)300,000 gas
Account creation (first use)$0.0005 (0.5 cents)250,000 gas
Contract deployment (1 KB)$0.035 (3.5 cents)1,750,000 gas
These costs assume a base fee of 2,000 attodollars/gas (2 × 10⁻¹⁵ USD per gas unit).
Economic UnitsTempo uses precise economic units for fee accounting:
  • Microdollars (μUSD): TIP-20 token units at 10⁻⁶ USD precision (6 decimals)
  • Attodollars (aUSD): Gas pricing units at 10⁻¹⁸ USD precision
See Gas Pricing for details.

​
Automatic Fee Conversion

When a user’s preferred fee token differs from the validator’s preferred token, the Fee AMM automatically converts between them: 
User pays:     100,000 USDC (user token)
         ↓
   Fee AMM:     Converts at 99.7% rate
         ↓
Validator receives: 99,700 pathUSD (validator token)
The conversion uses a simple linear pricing model with a 0.3% spread, ensuring minimal slippage and predictable costs.

​
Fee Collection Flow

​
1. Transaction Validation

When a transaction enters the mempool, the protocol:
  1. Resolves the user’s fee token preference
  2. Calculates the maximum fee amount: maxFee = gasLimit × baseFee
  3. Checks if the user has sufficient balance
  4. If conversion is needed, verifies Fee AMM has sufficient liquidity

​
2. Pre-Transaction Collection

Before executing the transaction, the protocol calls collectFeePreTx on the FeeManager: 
function collectFeePreTx(
    address user,
    address userToken,
    uint256 maxAmount
) external
This function:
  • Transfers maxAmount of userToken from the user to the FeeManager
  • If conversion is needed, verifies sufficient AMM liquidity
  • Temporarily holds the tokens in the FeeManager
See FeeManager.sol:38 for implementation.

​
3. Transaction Execution

The transaction executes normally, consuming gas based on the operations performed.

​
4. Post-Transaction Settlement

After execution, the protocol calls collectFeePostTx: 
function collectFeePostTx(
    address user,
    uint256 maxAmount,
    uint256 actualUsed,
    address userToken
) external
This function:
  • Calculates the refund: refund = maxAmount - actualUsed
  • Returns excess tokens to the user
  • Converts actualUsed tokens via the Fee AMM (if needed)
  • Credits the validator with converted tokens
See FeeManager.sol:62 for implementation.

​
5. Validator Distribution

Validators can withdraw their collected fees at any time: 
function distributeFees(address validator, address token) external
This transfers all collected fees for the specified token to the validator’s address. See FeeManager.sol:100 for implementation.

​
Fee Token Selection

​
User Preference

Users specify their fee token preference by calling: 
FeeManager(0xfeeC000000000000000000000000000000000000)
    .setUserToken(tokenAddress);
The preference persists across all future transactions from that address.

​
Validator Preference

Validators specify which token they want to receive fees in: 
FeeManager(0xfeeC000000000000000000000000000000000000)
    .setValidatorToken(tokenAddress);
Validators cannot change their fee token within the same block they’re producing. Attempting to call setValidatorToken from the block coinbase address reverts with CANNOT_CHANGE_WITHIN_BLOCK.

​
Default Token

If no preference is set:
  • Users default to pathUSD (0x20C0000000000000000000000000000000000000)
  • Validators default to pathUSD

​
Fee AMM Liquidity

For fee conversion to work, the Fee AMM must have sufficient liquidity in the relevant trading pair:
  • Pool structure: Directional pools for each (userToken → validatorToken) pair
  • Liquidity provision: Single-sided deposits (validator token only)
  • Rebalancing: Market participants can arbitrage via rebalanceSwap
See Fee AMM for details on liquidity provision and pool mechanics.

​
Gas Price Discovery

Tempo uses an EIP-1559-style base fee mechanism with stablecoin denomination:
  • Base fee: Dynamically adjusts based on block fullness
  • Target: 50% block utilization
  • Floor: Minimum base fee prevents spam attacks
See Gas Pricing for the complete pricing model.

​
State Creation Costs

Tempo significantly increases gas costs for state-creating operations to prevent spam attacks:
OperationStandard CostRationale
New storage slot (SSTORE 0→nonzero)250,000 gasPrevents state bloat attacks
Account creation (first nonce write)250,000 gasEconomic deterrent for mass account creation
Contract code (per byte)1,000 gasLinear pricing for code storage
Contract creation overhead500,000 gasCovers metadata storage (keccak, codesize)
At the target base fee, creating 1 TB of state costs approximately $50 million, providing strong economic protection against adversarial state growth. See TIP-1000 for the full specification.

​
Fee Token Introspection

Smart contracts can query which fee token is being used for the current transaction: 
interface IFeeManager {
    function getFeeToken() external view returns (address);
}

// Usage
address feeToken = IFeeManager(0xfeeC000000000000000000000000000000000000)
    .getFeeToken();
This enables contracts to implement fee-aware logic, such as:
  • Adjusting pricing based on the fee token
  • Routing decisions that consider fee costs
  • Logging fee token for off-chain indexing
See TIP-1007 for the specification.

​
Next Steps

Gas Pricing

Learn about attodollar denomination and base fee dynamics

Fee AMM

Understand automatic stablecoin conversion mechanics

Stablecoin Fees

Guide to paying gas in USD stablecoins

TIP-1000

State creation cost specification