📝Contract Interactions

Core Functions

Mint

Supply underlying ERC-20 tokens to the protocol and receive mTokens in return. The amount of mTokens minted is determined by the current exchange rate. Before calling mint, the caller must have approved the mToken contract to transfer the underlying token via ERC20.approve().

To skip the separate approve step, use mintWithPermit if the underlying token supports EIP-2612 permits.

function mint(uint mintAmount) external returns (uint)

Parameter	Type	Description
mintAmount	uint	The amount of underlying tokens to supply
returns	uint	0 on success, otherwise an Error code

function mintWithPermit(
    uint mintAmount,
    uint deadline,
    uint8 v,
    bytes32 r,
    bytes32 s
) external returns (uint)

Parameter	Type	Description
mintAmount	uint	The amount of underlying tokens to supply
deadline	uint	The permit signature deadline
v	uint8	The recovery byte of the permit signature
r	bytes32	Half of the ECDSA permit signature pair
s	bytes32	Half of the ECDSA permit signature pair
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
EIP20Interface underlying = EIP20Interface(mToken.underlying());

// Approve the mToken contract to spend underlying
uint mintAmount = 100e18;
underlying.approve(address(mToken), mintAmount);

// Mint mTokens
uint err = mToken.mint(mintAmount);
require(err == 0, "mint failed");

---

Redeem

Redeem mTokens in exchange for the underlying asset. The amount of underlying returned is determined by the current exchange rate. Pass type(uint).max to redeem your entire mToken balance.

function redeem(uint redeemTokens) external returns (uint)

Parameter	Type	Description
redeemTokens	uint	The number of mTokens to redeem, or type(uint).max for the full balance
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
uint err = mToken.redeem(50e8);
require(err == 0, "redeem failed");

---

Redeem Underlying

Redeem mTokens in exchange for a specified amount of the underlying asset. The protocol calculates how many mTokens to burn based on the current exchange rate. Pass type(uint).max to redeem all underlying.

function redeemUnderlying(uint redeemAmount) external returns (uint)

Parameter	Type	Description
redeemAmount	uint	The amount of underlying tokens to receive, or type(uint).max for the full balance
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
uint err = mToken.redeemUnderlying(100e18);
require(err == 0, "redeemUnderlying failed");

---

Borrow

Borrow underlying tokens from the protocol. The caller must have entered a market with sufficient collateral via the Comptroller's enterMarkets function before borrowing.

function borrow(uint borrowAmount) external returns (uint)

Parameter	Type	Description
borrowAmount	uint	The amount of underlying tokens to borrow
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
uint err = mToken.borrow(50e18);
require(err == 0, "borrow failed");

---

Repay Borrow

Repay a borrow position. The caller must approve the mToken contract to transfer the underlying token before calling. Pass type(uint).max as repayAmount to repay the entire outstanding balance.

function repayBorrow(uint repayAmount) external returns (uint)

Parameter	Type	Description
repayAmount	uint	The amount of underlying to repay, or type(uint).max for the full balance
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
EIP20Interface underlying = EIP20Interface(mToken.underlying());
uint repayAmount = 50e18;

underlying.approve(address(mToken), repayAmount);
uint err = mToken.repayBorrow(repayAmount);
require(err == 0, "repayBorrow failed");

---

Repay Borrow Behalf

Repay a borrow position on behalf of another account.

function repayBorrowBehalf(address borrower, uint repayAmount) external returns (uint)

Parameter	Type	Description
borrower	address	The account whose borrow to repay
repayAmount	uint	The amount of underlying to repay, or type(uint).max for the full balance
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...);
EIP20Interface underlying = EIP20Interface(mToken.underlying());
uint repayAmount = 50e18;
address borrower = 0x...; // The account whose borrow to repay

underlying.approve(address(mToken), repayAmount);
uint err = mToken.repayBorrowBehalf(borrower, repayAmount);
require(err == 0, "repayBorrowBehalf failed");

---

Liquidate Borrow

Liquidate an underwater borrower's position. The caller repays a portion of the borrower's debt and receives their collateral mTokens at a discount. The maximum repayable amount is determined by the Comptroller's closeFactorMantissa.

function liquidateBorrow(
    address borrower,
    uint repayAmount,
    MTokenInterface mTokenCollateral
) external returns (uint)

Parameter	Type	Description
borrower	address	The account to liquidate
repayAmount	uint	The amount of underlying to repay on behalf of the borrower. Unlike repayBorrow, type(uint).max is not supported - it returns error code INVALID_CLOSE_AMOUNT_REQUESTED.
mTokenCollateral	MTokenInterface	The mToken collateral to seize from the borrower
returns	uint	0 on success, otherwise an Error code

Solidity

MErc20 mToken = MErc20(0x...); // The borrowed market
MErc20 collateral = MErc20(0x...); // The collateral market
EIP20Interface underlying = EIP20Interface(mToken.underlying());
address borrower = 0x...; // The underwater account
uint repayAmount = 100e18;

underlying.approve(address(mToken), repayAmount);
uint err = mToken.liquidateBorrow(borrower, repayAmount, collateral);
require(err == 0, "liquidateBorrow failed");

---

Seize

Transfer collateral mTokens from a borrower to a liquidator. This function is called internally by the borrowed mToken's liquidateBorrow to seize collateral from the collateral mToken. It should not be called directly by end users.

function seize(address liquidator, address borrower, uint seizeTokens) external returns (uint)

Parameter	Type	Description
liquidator	address	The account receiving seized mTokens
borrower	address	The account being liquidated
seizeTokens	uint	The number of mTokens to seize
returns	uint	0 on success, otherwise an Error code

---

Add Reserves

Add underlying tokens to the protocol's reserves for a market.

function _addReserves(uint addAmount) external returns (uint)

Parameter	Type	Description
addAmount	uint	The amount of underlying to add to reserves
returns	uint	0 on success, otherwise an Error code

---

ERC-20 Functions

mTokens implement the standard ERC-20 interface. Transfers of mTokens are checked by the Comptroller - a transfer will fail if it would cause the sender's position to become undercollateralized.

function transfer(address dst, uint256 amount) external returns (bool)
function transferFrom(address src, address dst, uint256 amount) external returns (bool)
function approve(address spender, uint256 amount) external returns (bool)
function allowance(address owner, address spender) external view returns (uint256)
function balanceOf(address owner) external view returns (uint256)

---

Query Functions

Underlying

Returns the address of the underlying ERC-20 token for this mToken market.

function underlying() external view returns (address)

---

Exchange Rate

The exchange rate determines how many underlying tokens each mToken is worth. As interest accrues, the exchange rate increases, meaning each mToken is redeemable for a growing amount of underlying.

The exchange rate is scaled by 1e(18 - 8 + underlyingDecimals). mTokens always have 8 decimals. For example, an exchange rate of 2e26 for an underlying with 18 decimals means 1 mToken (1e8 units) = 2 underlying tokens (2e18 units).

Formula: exchangeRate = (totalCash + totalBorrows - totalReserves) / totalSupply

function exchangeRateCurrent() public returns (uint)

Accrues interest and returns the up-to-date exchange rate.

function exchangeRateStored() public view returns (uint)

Returns the exchange rate as of the last accrual (no state change, gas-efficient for reads).

---

Balance Of Underlying

Returns the mToken holder's balance denominated in the underlying asset, by applying the current exchange rate. This call accrues interest.

function balanceOfUnderlying(address owner) external returns (uint)

Parameter	Type	Description
owner	address	The account to query
returns	uint	The underlying token balance

---

Get Account Snapshot

Returns a snapshot of the account's current state without modifying storage.

function getAccountSnapshot(address account) external view returns (uint, uint, uint, uint)

Parameter	Type	Description
account	address	The account to query
returns	(uint, uint, uint, uint)	(error, mTokenBalance, borrowBalance, exchangeRateMantissa)

---

Borrow Balance

function borrowBalanceCurrent(address account) external returns (uint)

Accrues interest and returns the account's current borrow balance (including interest).

function borrowBalanceStored(address account) public view returns (uint)

Returns the stored borrow balance without accruing interest (gas-efficient for reads).

Parameter	Type	Description
account	address	The account to query
returns	uint	The borrow balance

---

Interest Rates

function borrowRatePerTimestamp() external view returns (uint)

Returns the current borrow interest rate per second, scaled by 1e18.

function supplyRatePerTimestamp() external view returns (uint)

Returns the current supply interest rate per second, scaled by 1e18.

---

Total Borrows

function totalBorrowsCurrent() external returns (uint)

Accrues interest and returns the total outstanding borrows for the market.

---

Get Cash

function getCash() external view returns (uint)

Returns the amount of underlying tokens held by the mToken contract (available liquidity).

---

Total Supply

function totalSupply() public view returns (uint)

Returns the total number of mTokens in existence.

---

Total Reserves

function totalReserves() public view returns (uint)

Returns the total reserves held by the market.

---

Reserve Factor

function reserveFactorMantissa() public view returns (uint)

Returns the current reserve factor, scaled by 1e18. This is the fraction of interest that goes to reserves.

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Accrue Interest

function accrueInterest() public returns (uint)

Applies accrued interest to total borrows and reserves. Called automatically by most state-changing functions, but can be called manually to bring the market up to date.

| returns | uint | 0 on success, otherwise an Error code |

---

Events

Event	Parameters
Mint	address minter, uint mintAmount, uint mintTokens
Redeem	address redeemer, uint redeemAmount, uint redeemTokens
Borrow	address borrower, uint borrowAmount, uint accountBorrows, uint totalBorrows
RepayBorrow	address payer, address borrower, uint repayAmount, uint accountBorrows, uint totalBorrows
LiquidateBorrow	address liquidator, address borrower, uint repayAmount, address mTokenCollateral, uint seizeTokens
AccrueInterest	uint cashPrior, uint interestAccumulated, uint borrowIndex, uint totalBorrows
Transfer	address indexed from, address indexed to, uint amount
Approval	address indexed owner, address indexed spender, uint amount
NewReserveFactor	uint oldReserveFactorMantissa, uint newReserveFactorMantissa
ReservesAdded	address benefactor, uint addAmount, uint newTotalReserves
ReservesReduced	address admin, uint reduceAmount, uint newTotalReserves
NewPendingAdmin	address oldPendingAdmin, address newPendingAdmin
NewAdmin	address oldAdmin, address newAdmin
NewComptroller	ComptrollerInterface oldComptroller, ComptrollerInterface newComptroller
NewMarketInterestRateModel	InterestRateModel oldInterestRateModel, InterestRateModel newInterestRateModel
NewProtocolSeizeShare	uint oldProtocolSeizeShareMantissa, uint newProtocolSeizeShareMantissa
Failure	uint error, uint info, uint detail

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Error Codes

All mToken functions that return a uint use 0 to indicate success. Non-zero values correspond to the following errors:

Code	Name	Description
0	NO_ERROR	Operation succeeded
1	UNAUTHORIZED	Caller is not authorized
2	BAD_INPUT	Invalid parameter provided
3	COMPTROLLER_REJECTION	Comptroller rejected the operation (e.g. insufficient collateral)
4	COMPTROLLER_CALCULATION_ERROR	Internal comptroller calculation error
5	INTEREST_RATE_MODEL_ERROR	Interest rate model returned an error
6	INVALID_ACCOUNT_PAIR	Invalid liquidation - liquidator and borrower are the same
7	INVALID_CLOSE_AMOUNT_REQUESTED	Liquidation close amount is invalid
8	INVALID_COLLATERAL_FACTOR	Invalid collateral factor
9	MATH_ERROR	Internal math error
10	MARKET_NOT_FRESH	Market interest has not been accrued to the current block
11	MARKET_NOT_LISTED	Market is not listed in the Comptroller
12	TOKEN_INSUFFICIENT_ALLOWANCE	Caller has not approved enough underlying tokens
13	TOKEN_INSUFFICIENT_BALANCE	Caller does not have enough underlying tokens
14	TOKEN_INSUFFICIENT_CASH	Market does not have enough liquidity
15	TOKEN_TRANSFER_IN_FAILED	Underlying token transfer into the market failed
16	TOKEN_TRANSFER_OUT_FAILED	Underlying token transfer out of the market failed

Errors are also emitted via the Failure(uint error, uint info, uint detail) event, where info provides more specific context about what failed. See the Failure Info section below.

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Failure Info

The info field in the Failure event provides granular context. These correspond to the FailureInfo enum:

Code	Name
0	ACCEPT_ADMIN_PENDING_ADMIN_CHECK
1	ACCRUE_INTEREST_ACCUMULATED_INTEREST_CALCULATION_FAILED
2	ACCRUE_INTEREST_BORROW_RATE_CALCULATION_FAILED
3	ACCRUE_INTEREST_NEW_BORROW_INDEX_CALCULATION_FAILED
4	ACCRUE_INTEREST_NEW_TOTAL_BORROWS_CALCULATION_FAILED
5	ACCRUE_INTEREST_NEW_TOTAL_RESERVES_CALCULATION_FAILED
6	ACCRUE_INTEREST_SIMPLE_INTEREST_FACTOR_CALCULATION_FAILED
7	BORROW_ACCUMULATED_BALANCE_CALCULATION_FAILED
8	BORROW_ACCRUE_INTEREST_FAILED
9	BORROW_CASH_NOT_AVAILABLE
10	BORROW_FRESHNESS_CHECK
11	BORROW_NEW_TOTAL_BALANCE_CALCULATION_FAILED
12	BORROW_NEW_ACCOUNT_BORROW_BALANCE_CALCULATION_FAILED
13	BORROW_MARKET_NOT_LISTED
14	BORROW_COMPTROLLER_REJECTION
15	LIQUIDATE_ACCRUE_BORROW_INTEREST_FAILED
16	LIQUIDATE_ACCRUE_COLLATERAL_INTEREST_FAILED
17	LIQUIDATE_COLLATERAL_FRESHNESS_CHECK
18	LIQUIDATE_COMPTROLLER_REJECTION
19	LIQUIDATE_COMPTROLLER_CALCULATE_AMOUNT_SEIZE_FAILED
20	LIQUIDATE_CLOSE_AMOUNT_IS_UINT_MAX
21	LIQUIDATE_CLOSE_AMOUNT_IS_ZERO
22	LIQUIDATE_FRESHNESS_CHECK
23	LIQUIDATE_LIQUIDATOR_IS_BORROWER
24	LIQUIDATE_REPAY_BORROW_FRESH_FAILED
25	LIQUIDATE_SEIZE_BALANCE_INCREMENT_FAILED
26	LIQUIDATE_SEIZE_BALANCE_DECREMENT_FAILED
27	LIQUIDATE_SEIZE_COMPTROLLER_REJECTION
28	LIQUIDATE_SEIZE_LIQUIDATOR_IS_BORROWER
29	LIQUIDATE_SEIZE_TOO_MUCH
30	MINT_ACCRUE_INTEREST_FAILED
31	MINT_COMPTROLLER_REJECTION
32	MINT_EXCHANGE_CALCULATION_FAILED
33	MINT_EXCHANGE_RATE_READ_FAILED
34	MINT_FRESHNESS_CHECK
35	MINT_NEW_ACCOUNT_BALANCE_CALCULATION_FAILED
36	MINT_NEW_TOTAL_SUPPLY_CALCULATION_FAILED
37	MINT_TRANSFER_IN_FAILED
38	MINT_TRANSFER_IN_NOT_POSSIBLE
39	REDEEM_ACCRUE_INTEREST_FAILED
40	REDEEM_COMPTROLLER_REJECTION
41	REDEEM_EXCHANGE_TOKENS_CALCULATION_FAILED
42	REDEEM_EXCHANGE_AMOUNT_CALCULATION_FAILED
43	REDEEM_EXCHANGE_RATE_READ_FAILED
44	REDEEM_FRESHNESS_CHECK
45	REDEEM_NEW_ACCOUNT_BALANCE_CALCULATION_FAILED
46	REDEEM_NEW_TOTAL_SUPPLY_CALCULATION_FAILED
47	REDEEM_TRANSFER_OUT_NOT_POSSIBLE
48	REDUCE_RESERVES_ACCRUE_INTEREST_FAILED
49	REDUCE_RESERVES_ADMIN_CHECK
50	REDUCE_RESERVES_CASH_NOT_AVAILABLE
51	REDUCE_RESERVES_FRESH_CHECK
52	REDUCE_RESERVES_VALIDATION
53	REPAY_BEHALF_ACCRUE_INTEREST_FAILED
54	REPAY_BORROW_ACCRUE_INTEREST_FAILED
55	REPAY_BORROW_ACCUMULATED_BALANCE_CALCULATION_FAILED
56	REPAY_BORROW_COMPTROLLER_REJECTION
57	REPAY_BORROW_FRESHNESS_CHECK
58	REPAY_BORROW_NEW_ACCOUNT_BORROW_BALANCE_CALCULATION_FAILED
59	REPAY_BORROW_NEW_TOTAL_BALANCE_CALCULATION_FAILED
60	REPAY_BORROW_TRANSFER_IN_NOT_POSSIBLE
61	SET_COLLATERAL_FACTOR_OWNER_CHECK
62	SET_COLLATERAL_FACTOR_VALIDATION
63	SET_COMPTROLLER_OWNER_CHECK
64	SET_INTEREST_RATE_MODEL_ACCRUE_INTEREST_FAILED
65	SET_INTEREST_RATE_MODEL_FRESH_CHECK
66	SET_INTEREST_RATE_MODEL_OWNER_CHECK
67	SET_MAX_ASSETS_OWNER_CHECK
68	SET_ORACLE_MARKET_NOT_LISTED
69	SET_PENDING_ADMIN_OWNER_CHECK
70	SET_RESERVE_FACTOR_ACCRUE_INTEREST_FAILED
71	SET_RESERVE_FACTOR_ADMIN_CHECK
72	SET_RESERVE_FACTOR_FRESH_CHECK
73	SET_RESERVE_FACTOR_BOUNDS_CHECK
74	TRANSFER_COMPTROLLER_REJECTION
75	TRANSFER_NOT_ALLOWED
76	TRANSFER_NOT_ENOUGH
77	TRANSFER_TOO_MUCH
78	ADD_RESERVES_ACCRUE_INTEREST_FAILED
79	ADD_RESERVES_FRESH_CHECK
80	ADD_RESERVES_TRANSFER_IN_NOT_POSSIBLE
81	SET_PROTOCOL_SEIZE_SHARE_ACCRUE_INTEREST_FAILED
82	SET_PROTOCOL_SEIZE_SHARE_OWNER_CHECK
83	SET_PROTOCOL_SEIZE_SHARE_FRESH_CHECK