App

Compound Presidio

Compound v2 (a.k.a. Presidio) is a set of smart contracts deployed on the Ethereum blockchain, which allows supplying and borrowing of ERC-20 tokens. This page details the on-chain function "ABI" for developing smart contracts or building Web3-enabled dApps. (Looking for the v1 docs? View Legacy Documentation)

For information on the Compound API, please visit the Compound API docs.

Getting Started

The Compound Protocol v2 is currently deployed on the following networks:

Mainnet

Contract ABI Address
cBAT JSON
0x6c8c6b02e7b2be14d4fa6022dfd6d75921d90e4e
cDAI JSON
0xf5dce57282a584d2746faf1593d3121fcac444dc
cETH JSON
0x4ddc2d193948926d02f9b1fe9e1daa0718270ed5
cREP JSON
0x158079ee67fce2f58472a96584a73c7ab9ac95c1
cUSDC JSON
0x39aa39c021dfbae8fac545936693ac917d5e7563
cZRX JSON
0xb3319f5d18bc0d84dd1b4825dcde5d5f7266d407
Comptroller JSON
0x3d9819210a31b4961b30ef54be2aed79b9c9cd3b
PriceOracle JSON
0x02557a5e05defeffd4cae6d83ea3d173b272c904
WhitePaperInterestRateModel JSON
0xc64c4cba055efa614ce01f4bad8a9f519c4f8fab
WhitePaperInterestRateModel JSON
0xbae04cbf96391086dc643e842b517734e214d698
WhitePaperInterestRateModel JSON
0xa1046abfc2598f48c44fb320d281d3f3c0733c9a

Rinkeby

Contract ABI Address
cBAT JSON
0xebf1a11532b93a529b5bc942b4baa98647913002
cDAI JSON
0x6d7f0754ffeb405d23c51ce938289d4835be3b14
cETH JSON
0xd6801a1dffcd0a410336ef88def4320d6df1883e
cREP JSON
0xebe09eb3411d18f4ff8d859e096c533cac5c6b60
cUSDC JSON
0x5b281a6dda0b271e91ae35de655ad301c976edb1
cZRX JSON
0x52201ff1720134bbbbb2f6bc97bf3715490ec19b
Comptroller JSON
0x2eaa9d77ae4d8f9cdd9faacd44016e746485bddb
PriceOracle JSON
0xd2b1eca822550d9358e97e72c6c1a93ae28408d0
WhitePaperInterestRateModel JSON
0x1a43bfd39b15dcf444e17ab408c4b5be32deb7f5
WhitePaperInterestRateModel JSON
0x6330d442a2d7ee4dc66c0adb9969e8702aefc9fe
WhitePaperInterestRateModel JSON
0xe12630c8fdd7d0096c9cd72cd228598aebe58795

Kovan

Contract ABI Address
cBAT JSON
0x39f91488647f5f0a6c967463f8c3c02cdc5c3f5b
cDAI JSON
0xb6b09fbffba6a5c4631e5f7b2e3ee183ac259c0d
cETH JSON
0xd96dbd1d1a0bfdae6ada7f5c1cb6eaa485c9ab78
cREP JSON
0x15de1ca698b510948a3812f041446a4acf29bcf7
cZRX JSON
0xa085e0936f5ce33ddf963294448a3d9dcfeb2bbf
Comptroller JSON
0x3ca5a0e85ad80305c2d2c4982b2f2756f1e747a5
PriceOracle JSON
0x4b6419f70fbee1661946f165563c1de0d35e618c
StableCoinInterestRateModel JSON
0xd9f3595d7a16b3791823ce709a5dadab6dae9021
StandardInterestRateModel JSON
0xd219bbfc695dcd5d57bbcf9de7316fdf789ef493

Ropsten

Contract ABI Address
cBAT JSON
0x39f91488647f5f0a6c967463f8c3c02cdc5c3f5b
cDAI JSON
0xb6b09fbffba6a5c4631e5f7b2e3ee183ac259c0d
cETH JSON
0xd96dbd1d1a0bfdae6ada7f5c1cb6eaa485c9ab78
cREP JSON
0x15de1ca698b510948a3812f041446a4acf29bcf7
cZRX JSON
0xa085e0936f5ce33ddf963294448a3d9dcfeb2bbf
Comptroller JSON
0x3ca5a0e85ad80305c2d2c4982b2f2756f1e747a5
PriceOracle JSON
0x4b6419f70fbee1661946f165563c1de0d35e618c
StableCoinInterestRateModel JSON
0xd9f3595d7a16b3791823ce709a5dadab6dae9021
StandardInterestRateModel JSON
0xd219bbfc695dcd5d57bbcf9de7316fdf789ef493

cTokens

Every asset supported by the Compound Protocol is now integrated through a cToken smart contract, which is an EIP-20 compliant representation of balances supplied to the protocol. Users supply to the protocol by minting tokens (cTokens), which strictly increase in value relative to their underlying asset.

cTokens are the primary way of interacting with the Compound Protocol. Each cToken contract creates its own money market. When a user mints, redeems, borrows, repays a borrow, liquidates a borrow, or transfers cTokens, she will do so using the cToken contract.

There are currently two types of cTokens: CErc20 and CEther. Though both types expose the EIP-20 interface, CErc20 wraps an underlying ERC-20 asset, while CEther simply wraps Ether itself. As such, the core functions which involve transferring an asset into the protocol have slightly different interfaces depending on the type, each of which is shown below.

Mint

The mint function transfers an asset into the money market, which begins accumulating interest based on the current supply rate for the asset. The number of tokens minted is the amount of underlying asset being provided divided by the current exchange rate.

Mint is analagous to supply from the Compound v1 Protocol.

CErc20
function mint(uint mintAmount) returns (uint)
  • msg.sender - The account which shall supply the asset, and own the minted cTokens.
  • mintAmount - The amount of the asset to be supplied, in units of the underlying asset.
  • RETURN - 0 on success, otherwise an error code.

Before supplying an asset, users must first approve the cToken to access their token balance.

CEther
function mint() payable
  • msg.value - The amount of ether to be supplied, in wei.
  • msg.sender - The account which shall supply the ether, and own the minted cTokens.
  • RETURN - No return, reverts on error.
Solidity
Erc20 underlying = Erc20(0xToken...);     // get a handle for the underlying asset contract
CErc20 cToken = CErc20(0x3FDA...);        // get a handle for the corresponding cToken contract
underlying.approve(address(cToken), 100); // approve the transfer
assert(cToken.mint(100) == 0);            // mint the cTokens and assert there is no error
Web3 1.0
const cToken = CEther.at(0x3FDB...);
await cToken.methods.mint().send({from: myAccount, value: 50});

Redeem

The redeem function transfers the underlying asset from the money market to the user in exchange for previously minted cTokens. The amount of underlying redeemed is the number of cTokens multiplied by the current Exchange Rate. The amount redeemed must be less than the user's account liquidity and the market's available liquidity.

Redeem is analagous to withdraw from the Compound v1 Protocol.

CErc20 / CEther
function redeem(uint redeemTokens) returns (uint)
  • msg.sender - The account to which redeemed funds shall be transferred.
  • redeemTokens - The number of cTokens to be redeemed.
  • RETURN - 0 on success, otherwise an error code.
Solidity
CEther cToken = CEther(0x3FDB...);
require(cToken.redeem(7) == 0, "something went wrong");
Web3 1.0
const cToken = CErc20.at(0x3FDA...);
cToken.methods.redeem(1).send({from: ...});

Redeem Underlying

The redeem underlying function transfers the underlying asset from the money market to the user in exchange for previously minted cTokens. The number of cTokens redeemed is the amount of underlying divided by the current Exchange Rate. The amount redeemed must be less than the user's account liquidity and the market's available liquidity.

CErc20 / CEther
function redeemUnderlying(uint redeemAmount) returns (uint)
  • msg.sender - The account to which redeemed funds shall be transferred.
  • redeemAmount - The amount of underlying to be redeemed.
  • RETURN - 0 on success, otherwise an error code.
Solidity
CEther cToken = CEther(0x3FDB...);
require(cToken.redeemUnderlying(50) == 0, "something went wrong");
Web3 1.0
const cToken = CErc20.at(0x3FDA...);
cToken.methods.redeemUnderlying(10).send({from: ...});

Borrow

The borrow function transfers an asset from the money market to the user, and creates a borrow balance which begins accumulating interest based on the borrow rate for the asset.

The amount borrowed must be less than the user's borrow capacity and the market's available liquidity. Users must maintain a collateral requirement to avoid liquidation.

Note that the borrower will receive a transfer of the underlying asset. For CEther, this will be ether and thus the borrower must be payable (for Solidity).

CErc20 / CEther
function borrow(uint borrowAmount) returns (uint)
  • msg.sender - The account to which borrowed funds shall be transferred.
  • borrowAmount - The amount of the underlying asset to be borrowed.
  • RETURN - 0 on success, otherwise an error code.
Solidity
CErc20 cToken = CErc20(0x3FDA...);
require(cToken.borrow(100) == 0, "got collateral?");
Web3 1.0
const cToken = CEther.at(0x3FDB...);
await cToken.methods.borrow(50).send({from: 0xMyAccount});

Repay Borrow

The repay function transfers an asset into the money market, reducing the user's borrow balance.

CErc20
function repayBorrow(uint repayAmount) returns (uint)
  • msg.sender - The account which borrowed the asset, and shall repay the borrow.
  • repayAmount - The amount of the underlying borrowed asset to be repaid. A value of -1 (i.e. 2256 - 1) can be used to repay the full amount.
  • RETURN - 0 on success, otherwise an error code.

Before supplying an asset, users must first approve the cToken to access their token balance.

CEther
function repayBorrow() payable
  • msg.value - The amount of ether to be repaid, in wei.
  • msg.sender - The account which borrowed the asset, and shall repay the borrow.
  • RETURN - No return, reverts on error.
Solidity
CEther cToken = CEther(0x3FDB...);
require(cToken.repayBorrow.value(100)() == 0, "transfer approved?");
Web3 1.0
const cToken = CErc20.at(0x3FDA...);
cToken.methods.repayBorrow(10000).send({from: ...});

Repay Borrow Behalf

The repay function transfers an asset into the money market, reducing the user's borrow balance.

CErc20
function repayBorrowBehalf(address borrower, uint repayAmount) returns (uint)
  • msg.sender - The account which shall repay the borrow.
  • borrower - The account which borrowed the asset to be repaid.
  • repayAmount - The amount of the underlying borrowed asset to be repaid. A value of -1 (i.e. 2256 - 1) can be used to repay the full amount.
  • RETURN - 0 on success, otherwise an error code.

Before supplying an asset, users must first approve the cToken to access their token balance.

CEther
function repayBorrowBehalf(address borrower) payable
  • msg.value - The amount of ether to be repaid, in wei.
  • msg.sender - The account which shall repay the borrow.
  • borrower - The account which borrowed the asset to be repaid.
  • RETURN - No return, reverts on error.
Solidity
CEther cToken = CEther(0x3FDB...);
require(cToken.repayBorrowBehalf.value(100)(0xBorrower) == 0, "transfer approved?");
Web3 1.0
const cToken = CErc20.at(0x3FDA...);
await cToken.methods.repayBorrowBehalf(0xBorrower, 10000).send({from: 0xPayer});

Liquidate Borrow

A user who has negative account liquidity is subject to liquidation by other users of the protocol to return his/her account liquidity back to positive (i.e. above the collateral requirement). When a liquidation occurs, a liquidator may repay some or all of an outstanding borrow on behalf of a borrower and in return receive a discounted amount of collateral held by the borrower; this discount is defined as the liquidation incentive.

A liquidator may close up to a certain fixed percentage (i.e. close factor) of any individual outstanding borrow of the underwater account. Unlike in v1, liquidators must interact with each cToken contract in which they wish to repay a borrow and seize another asset as collateral. When collateral is seized, the liquidator is transferred cTokens, which they may redeem the same as if they had supplied the asset themselves. Users must approve each cToken contract before calling liquidate (i.e. on the borrowed asset which they are repaying), as they are transferring funds into the contract.

CErc20
function liquidateBorrow(address borrower, uint repayAmount, address cTokenCollateral) returns (uint)
  • msg.sender - The account which shall liquidate the borrower by repaying their debt and seizing their collateral.
  • borrower - The account with negative account liquidity that shall be liquidated.
  • repayAmount - The amount of the borrowed asset to be repaid and converted into collateral, specified in units of the underlying borrowed asset.
  • cTokenCollateral - The address of the cToken currently held as collateral by a borrower, that the liquidator shall seize.
  • RETURN - 0 on success, otherwise an error code.

Before supplying an asset, users must first approve the cToken to access their token balance.

CEther
function liquidateBorrow(address borrower, address cTokenCollateral) payable
  • msg.value - The amount of ether to be repaid and converted into collateral, in wei.
  • msg.sender - The account which shall liquidate the borrower by repaying their debt and seizing their collateral.
  • borrower - The account with negative account liquidity that shall be liquidated.
  • cTokenCollateral - The address of the cToken currently held as collateral by a borrower, that the liquidator shall seize.
  • RETURN - No return, reverts on error.
Solidity
CEther cToken = CEther(0x3FDB...);
CErc20 cTokenCollateral = CErc20(0x3FDA...);
require(cToken.liquidateBorrow.value(100)(0xBorrower, cTokenCollateral) == 0, "borrower underwater??");
Web3 1.0
const cToken = CErc20.at(0x3FDA...);
const cTokenCollateral = CEther.at(0x3FDB...);
await cToken.methods.liquidateBorrow(0xBorrower, 33, cTokenCollateral).send({from: 0xLiquidator});

Key Events

Event Description
Mint(address minter, uint mintTokens, uint mintAmount) Emitted upon a successful Mint.
Redeem(address redeemer, uint redeemTokens, uint redeemAmount) Emitted upon a successful Redeem.
Borrow(address borrower, uint borrowAmount, uint accountBorrows, uint totalBorrows) Emitted upon a successful Borrow.
RepayBorrow(address payer, address borrower, uint repayAmount, uint accountBorrows, uint totalBorrows) Emitted upon a successful Repay Borrow.
LiquidateBorrow(address liquidator, address borrower, uint repayAmount, address cTokenCollateral, uint seizeTokens) Emitted upon a successful Liquidate Borrow.

Error Codes

Error Code Error Name Further Details
0 NO_ERROR Not a failure.
1 UNAUTHORIZED The sender is not authorized to perform this action.
2 BAD_INPUT An invalid argument was supplied by the caller.
3 COMPTROLLER_REJECTION The action would violate the comptroller policy.
4 COMPTROLLER_CALCULATION_ERROR An internal calculation has failed in the comptroller.
5 INTEREST_RATE_MODEL_ERROR The interest rate model returned an invalid value.
6 INVALID_ACCOUNT_PAIR The specified combination of accounts is invalid.
7 INVALID_CLOSE_AMOUNT_REQUESTED The amount to liquidate is invalid.
8 INVALID_COLLATERAL_FACTOR The collateral factor is invalid.
9 MATH_ERROR A math calculation error occurred.
10 MARKET_NOT_FRESH Interest has not been properly accrued.
11 MARKET_NOT_LISTED The market is not currently listed by its comptroller.
12 TOKEN_INSUFFICIENT_ALLOWANCE ERC-20 contract must *allow* Money Market contract to call `transferFrom`. The current allowance is either 0 or less than the requested supply, repayBorrow or liquidate amount.
13 TOKEN_INSUFFICIENT_BALANCE Caller does not have sufficient balance in the ERC-20 contract to complete the desired action.
14 TOKEN_INSUFFICIENT_CASH The market does not have a sufficient cash balance to complete the transaction. You may attempt this transaction again later.
15 TOKEN_TRANSFER_IN_FAILED Failure in ERC-20 when transfering token into the market.
16 TOKEN_TRANSFER_OUT_FAILED Failure in ERC-20 when transfering token out of the market.

Failure Info

Failure Code Failure 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

cToken Helpers

In addition to the core market functions, the cToken contracts implement a number of helper functions to aid developers in building on top of the protocol.

Exchange Rate

Each cToken is convertible into an ever increasing quantity of the underlying asset, as interest accrues in the market. The exchange rate between a cToken and the underlying asset is equal to:

exchangeRate = (getCash() + totalBorrows() - totalReserves()) / totalSupply()
CErc20 / CEther
function exchangeRateCurrent() returns (uint)
  • RETURN - The current exchange rate as an unsigned integer, scaled by 1e18.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint exchangeRateMantissa = cToken.exchangeRateCurrent();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const exchangeRate = (await cToken.methods.exchangeRateCurrent().call()) / 1e18;

Tip: note the use of call vs. send to invoke the function from off-chain without incurring gas costs.

Get Cash

Cash is the amount of underlying balance owned by this cToken contract. One may query the total amount of cash currently available to this market.

CErc20 / CEther
function getCash() returns (uint)
  • RETURN - The quantity of underlying asset owned by the contract.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint cash = cToken.getCash();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const cash = (await cToken.methods.getCash().call());

Total Borrows

Total Borrows is the amount of underlying currently loaned out by the market, and the amount upon which interest is accumulated to suppliers of the market.

CErc20 / CEther
function totalBorrowsCurrent() returns (uint)
  • RETURN - The total amount of borrowed underlying, with interest.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint borrows = cToken.totalBorrowsCurrent();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const borrows = (await cToken.methods.totalBorrowsCurrent().call());

Borrow Balance

A user who borrows assets from the protocol is subject to accumulated interest based on the current borrow rate. Interest is accumulated every block and integrations may use this function to obtain the current value of a user's borrow balance with interest.

CErc20 / CEther
function borrowBalanceCurrent(address account) returns (uint)
  • account - The account which borrowed the assets.
  • RETURN - The user's current borrow balance (with interest) in units of the underlying asset.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint borrows = cToken.borrowBalanceCurrent(msg.caller);
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const borrows = await cToken.methods.borrowBalanceCurrent(account).call();

Borrow Rate

At any point in time one may query the contract to get the current borrow rate per block.

CErc20 / CEther
function borrowRatePerBlock() returns (uint)
  • RETURN - The current borrow rate as an unsigned integer, scaled by 1e18.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint borrowRateMantissa = cToken.borrowRatePerBlock();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const borrowRate = (await cToken.methods.borrowRatePerBlock().call()) / 1e18;

Total Supply

Total Supply is the number of tokens currently in circulation in this cToken market. It is part of the EIP-20 interface of the cToken contract.

CErc20 / CEther
function totalSupply() returns (uint)
  • RETURN - The total number of tokens in circulation for the market.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint tokens = cToken.totalSupply();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const tokens = (await cToken.methods.totalSupply().call());

Supply Balance

A user who supplies assets to the protocol receives tokens which accumulate interest based on the current supply rate. At any given time, the value of a token with interest may be queried via the exchange rate. The number of tokens owned by a particular user may also be queried, which is part of the EIP-20 interface of the cToken contract.

CErc20 / CEther
function balanceOf(address account) returns (uint)
  • account - The account to get the token balance of.
  • RETURN - The number of tokens currently owned by the account.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint tokens = cToken.balanceOf(msg.caller);
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const tokens = await cToken.methods.balanceOf(account).call();

Supply Balance Underlying

CTokens also have a convenience method for determining the supply balance in terms of the amount of underlying (i.e. supply balance multiplied by the exchange rate).

CErc20 / CEther
function balanceOfUnderlying(address account) returns (uint)
  • account - The account to get the underlying balance of.
  • RETURN - The amount of underlying currently owned by the account.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint tokens = cToken.balanceOfUnderlying(msg.caller);
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const tokens = await cToken.methods.balanceOfUnderlying(account).call();

Supply Rate

At any point in time one may query the contract to get the current supply rate per block. The supply rate is derived from the borrow rate, reserve factor, and the amount of total borrows.

CErc20 / CEther
function supplyRatePerBlock() returns (uint)
  • RETURN - The current supply rate as an unsigned integer, scaled by 1e18.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint supplyRateMantissa = cToken.supplyRatePerBlock();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const supplyRate = (await cToken.methods.supplyRatePerBlock().call()) / 1e18;

Total Reserves

Reserves are the equity accrued to the protocol itself, in order to fund its operation. Reserves also form part of the cash which may be loaned out to borrowers in the market. A small portion of borrower interest accrues into the protocol, determined by the reserve factor.

CErc20 / CEther
function totalReserves() returns (uint)
  • RETURN - The total amount of reserves held by the protocol.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint reserves = cToken.totalReserves();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const reserves = (await cToken.methods.totalReserves().call());

Reserve Factor

The reserve factor defines the small slice of interest that is accrued into reserves.

CErc20 / CEther
function reserveFactorMantissa() returns (uint)
  • RETURN - The current reserve factor as an unsigned integer, scaled by 1e18.
Solidity
CErc20 cToken = CToken(0x3FDA...);
uint reserveFactorMantissa = cToken.reserveFactorMantissa();
Web3 1.0
const cToken = CEther.at(0x3FDB...);
const reserveFactor = (await cToken.methods.reserveFactorMantissa().call()) / 1e18;

Comptroller

The comptroller contract manages the risk associated with the Compound Protocol v2. It is responsible for determining when account's are underwater and can be liquidated. It determines how much collateral can be seized in exchange for liquidating an underwater account. It also provides a defense mechanism to protect the protocol against unforeseen future attacks on the market.

In order to borrow from a market, users are required to supply collateral in some other market(s). Collateral protects the borrowed market, by incentivizing the borrower and/or a liquidator to repay debt. In v1, all markets had the same collateral factor. In addition, any market an account supplied to automatically became collateral for any borrows opened by that account.

In v2, we open the door for each market to determine what is sufficient collateral for a borrow of its asset. We also require that users explicitly enter the markets which they wish to either use as collateral or borrow from. This cuts down on the cost of supporting a large number of markets, while giving users the choice to not use all of their assets as collateral. The cost is a small bit of management overhead for users wishing to borrow, since they must now enter and exit markets.

Enter Markets

Enter into a list of markets - it is not an error to enter the same market more than once. In order to supply collateral or borrow in a market, it must be entered first.

Comptroller
function enterMarkets(address[] calldata cTokens) returns (uint[] memory)
  • msg.sender - The account which shall enter the given markets.
  • cTokens - The addresses of the cToken markets to enter.
  • RETURN - For each market, returns an error code indicating whether or not it was entered. Each is 0 on success, otherwise an error code.
Solidity
Comptroller troll = Comptroller(0xABCD...);
CToken[] memory cTokens = new CToken[](2);
cTokens[0] = CErc20(0x3FDA...);
cTokens[1] = CEther(0x3FDB...);
uint[] memory errors = troll.enterMarkets(cTokens);
Web3 1.0
const troll = Comptroller.at(0xABCD...);
const cTokens = [CErc20.at(0x3FDA...), CEther.at(0x3FDB...)];
const errors = await troll.methods.enterMarkets(cTokens).send({from: ...});

Exit Market

Exit a market - it is not an error to exit a market which is not currently entered. Exited markets will not count towards account liquidity calculations.

Comptroller
function exitMarket(address cToken) returns (uint)
  • msg.sender - The account which shall exit the given market.
  • cToken - The addresses of the cToken market to exit.
  • RETURN - 0 on success, otherwise an error code.
Solidity
Comptroller troll = Comptroller(0xABCD...);
uint error = troll.exitMarket(CToken(0x3FDA...));
Web3 1.0
const troll = Comptroller.at(0xABCD...);
const errors = await troll.methods.exitMarket(CEther.at(0x3FDB...)).send({from: ...});

Get Assets In

Get the list of markets an account is currently entered into. In order to supply collateral or borrow in a market, it must be entered first. Entered markets count towards account liquidity calculations.

Comptroller
function getAssetsIn(address account) view returns (address[] memory)
  • account - The account whose list of entered markets shall be queried.
  • RETURN - The address of each market which is currently entered into.
Solidity
Comptroller troll = Comptroller(0xABCD...);
address[] memory markets = troll.getAssetsIn(0xMyAccount);
Web3 1.0
const troll = Comptroller.at(0xABCD...);
const markets = await troll.methods.getAssetsIn(cTokens).call();

Get Account Liquidity

Within the Compound Protocol, account liquidity is defined as the total estimated ether value of an account's collateral (supply balances multiplied by the protocol collateral factor), minus the total value of that account's borrow balances. These values are calculated using only the markets which the account has entered into.

Users who do not have positive account liquidity do not have the ability to withdraw or borrow any assets until they bring their account liquidity back positive by supplying more assets or paying back outstanding borrows.

Sometimes account liquidity refers to a single signed value, rather than two unsigned values - however the Compound Protocol only deals with unsigned integers. A negative value for account liquidity also means the user is subject to liquidation to bring their account liquidity back to zero.

function getAccountLiquidity(address account) view returns (uint, uint, uint)
  • account - The account whose liquidity shall be calculated.
  • RETURN - Tuple of values (error, liquidity, shortfall). The error shall be 0 on success, otherwise an error code. A non-zero liquidity value indicates the account has available account liquidity. A non-zero shortfall value indicates the account is currently below his/her collateral requirement and is subject to liquidation. At most one of liquidity or shortfall shall be non-zero.
Solidity
Comptroller troll = Comptroller(0xABCD...);
(uint error, uint liquidity, uint shortfall) = troll.getAccountLiquidity(msg.caller);
require(error == 0, "join the Discord");
require(shortfall == 0, "account underwater");
require(liquidity > 0, "account has excess collateral");
Web3 1.0
const troll = Comptroller.at(0xABCD...);
const result = await troll.methods.getAccountLiquidity(0xBorrower).call();
const {0: error, 1: liquidity, 2: shortfall} = result;

Key Events

Event Description
MarketEntered(CToken cToken, address account) Emitted upon a successful Enter Market.
MarketExited(CToken cToken, address account) Emitted upon a successful Exit Market.

Error Codes

Error Code Error Name Further Details
0 NO_ERROR Not a failure.
1 UNAUTHORIZED The sender is not authorized to perform this action.
2 COMPTROLLER_MISMATCH Liquidation cannot be performed in markets with different comptrollers.
3 INSUFFICIENT_SHORTFALL The account does not have sufficient shortfall to perform this action.
4 INSUFFICIENT_LIQUIDITY The account does not have sufficient liquidity to perform this action.
5 INVALID_CLOSE_FACTOR The close factor is not valid.
6 INVALID_COLLATERAL_FACTOR The collateral factor is not valid.
7 INVALID_LIQUIDATION_INCENTIVE The liquidation incentive is invalid.
8 MARKET_NOT_ENTERED The market has not been entered by the account.
9 MARKET_NOT_LISTED The market is not currently listed by the comptroller.
10 MARKET_ALREADY_LISTED An admin tried to list the same market more than once.
11 MATH_ERROR A math calculation error occurred.
12 NONZERO_BORROW_BALANCE The action cannot be performed since the account carries a borrow balance.
13 PRICE_ERROR The comptroller could not obtain a required price of an asset.
14 REJECTION The comptroller rejects the action requested by the market.
15 SNAPSHOT_ERROR The comptroller could not get the account borrows and exchange rate from the market.
16 TOO_MANY_ASSETS Attempted to enter more markets than are currently supported.
17 TOO_MUCH_REPAY Attempted to repay more than is allowed by the protocol.

Failure Info

Failure Code Failure Name
0 ACCEPT_ADMIN_PENDING_ADMIN_CHECK
1 ACCEPT_PENDING_IMPLEMENTATION_ADDRESS_CHECK
2 EXIT_MARKET_BALANCE_OWED
3 EXIT_MARKET_REJECTION
4 SET_CLOSE_FACTOR_OWNER_CHECK
5 SET_CLOSE_FACTOR_VALIDATION
6 SET_COLLATERAL_FACTOR_OWNER_CHECK
7 SET_COLLATERAL_FACTOR_NO_EXISTS
8 SET_COLLATERAL_FACTOR_VALIDATION
9 SET_COLLATERAL_FACTOR_WITHOUT_PRICE
10 SET_IMPLEMENTATION_OWNER_CHECK
11 SET_LIQUIDATION_INCENTIVE_OWNER_CHECK
12 SET_LIQUIDATION_INCENTIVE_VALIDATION
13 SET_MAX_ASSETS_OWNER_CHECK
14 SET_PENDING_ADMIN_OWNER_CHECK
15 SET_PENDING_IMPLEMENTATION_OWNER_CHECK
16 SET_PRICE_ORACLE_OWNER_CHECK
17 SUPPORT_MARKET_EXISTS
18 SUPPORT_MARKET_OWNER_CHECK

Appendix

Supplementary discussion of some considerations for using the protocol. If you have other questions which are not answered here, please feel free to reach out for support.

Collateral

In order to borrow from the protocol, accounts must provide enough collateral. One of the greatest motivating factors for Compound v2: Presidio was the ability to set different collateral requirements, depending on the asset being borrowed. With Presidio, the protocol no longer has a global collateral requirement and instead opens it up to individual asset communities to determine what is sufficient collateral in order to borrow their asset.

More details about how this works now and how it will evolve will be coming in the next few weeks as we prepare for mainnet launch.

Exponential Math

The Compound smart contracts use a system of exponential math in order to represent fractional quantities with sufficient precision. Throughout the documentation and code we make reference to mantissas, which are unsigned integers scaled up by a factor of 1e18 from their nominal value. By using mantissas within our contracts, we may perform basic mathematical operations like multiplication and division at a higher resolution than working with the unscaled quantities directly as integers. To gain a better understanding of how this works, see Exponential.sol.

Gas Costs

The gas usage of the protocol functions may fluctuate by market and user. External calls, such as to underlying ERC-20 tokens, may use an arbitrary amount of gas. Any calculations that involve checking account liquidity, have gas costs that increase with the number of entered markets. Thus, while it can be difficult to provide any guarantees about costs, we provide the table below for guidance:

Function Typical Gas Cost
Mint < 90K
Redeem, Transfer < 250K if borrowing, otherwise < 90K
Borrow < 300K
Repay Borrow < 90K
Liquidate Borrow < 400K

Glossary

Term Description
Collateral Factor The amount of an asset that may be borrowed for each unit of collateral provided. The collateral factor is defined per market.
Close Factor The portion of a borrow in a single market that may be closed by a liquidator during a single liquidation. For example, if Joe borrows 100 ZRX and the close factor is 0.3, then a liquidator may close 30 ZRX. The close factor is globally defined across all markets.
Liquidation Incentive The additional collateral given to liquidators as an incentive to perform liquidation of underwater accounts. For example, if the liquidation incentive is 1.1, liquidators receive an extra 10% of the borrowers collateral for every unit they close. The liquidation incentive is globally defined across all markets.

Support

For support requests, please reach out to us in the #development channel in our Discord. We're happy to help out and grow the Compound community. Your questions help us improve, so please don't hesitate to ask if you can't find what you are looking for here.