API Index


swapExactAmountIn(tokenIn, tokenAmountIn, tokenOut, minAmountOut, maxPrice)->(tokenAmountOut, spotPriceAfter)

swapExactAmountOut(tokenIn, maxAmountIn, tokenOut, tokenAmountOut, maxPrice)->(tokenAmountIn, spotPriceAfter)

joinPool(poolAmountOut, [maxAmountsIn])

exitPool(poolAmountIn, [minAMountsOut])

joinswapExternAmountIn(tokenIn, tokenAmountIn, minPoolAmountOut)->(poolAmountOut)

exitswapExternAmountOut(tokenOut, tokenAmountOut, maxPoolAmountIn)->(poolAmountIn)

joinswapPoolAmountOut(tokenIn, poolAmountOut, maxAmountIn)->(tokenAmountIn)

exitswapPoolAmountIn(tokenOut, poolAmountIn, minAmountOut)->(tokenAmountOut)






bind(token, balance, denorm)

rebind(token, balance, denorm)



















Controller and View Functions


isBound(address T) -> (bool)

A bound token has a valid balance and weight. A token cannot be bound without valid parameters which will enable e.g. getSpotPrice in terms of other tokens. However, disabling isSwapPublic will disable any interaction with this token in practice (assuming there are no existing tokens in the pool, which can always exitPool).


getNumTokens() -> (uint)

How many tokens are bound to this pool.


getNormalizedWeight(address token) -> (uint)

The normalized weight of a token. The combined normalized weights of all tokens will sum up to 1. (Note: the actual sum may be 1 plus or minus a few wei due to division precision loss)


getController() -> (address)

Get the "controller" address, which can call CONTROL functions like rebind, setSwapFee, or finalize.


bind(address token, uint balance, uint denorm)

Binds the token with address token. Tokens will be pushed/pulled from caller to adjust match new balance. Token must not already be bound. balance must be a valid balance and denorm must be a valid denormalized weight. bind creates the token record and then calls rebind for updating pool weights and token transfers.

Possible errors:

  • ERR_NOT_CONTROLLER -- caller is not the controller

  • ERR_IS_BOUND -- T is already bound

  • ERR_IS_FINALIZED -- isFinalized() is true

  • ERR_ERC20_FALSE -- ERC20 token returned false

  • ERR_MAX_TOKENS -- Only 8 tokens are allowed per pool

  • unspecified error thrown by token


rebind(address token, uint balance, uint denorm)

Changes the parameters of an already-bound token. Performs the same validation on the parameters.


unbind(address token)

Unbinds a token, clearing all of its parameters. Exit fee is charged and the remaining balance is sent to caller.


setPublicSwap(bool isPublic)

Makes isPublicSwap return _publicSwap Requires caller to be controller and pool not to be finalized. Finalized pools always have public swap.



This makes the pool finalized. This is a one-way transition. bind, rebind, unbind, setSwapFee and setPublicSwap will all throw ERR_IS_FINALIZED after pool is finalized. This also switches isSwapPublic to true.


gulp(address token)

This syncs the internal balance of token within a pool with the actual balance registered on the ERC20 contract. This is useful to account for airdropped tokens or any tokens sent to the pool without using the join or joinSwap methods.


setSwapFee(uint swapFee)

Caller must be controller. Pool must NOT be finalized.


isFinalized() -> (bool)

The finalized state lets users know that the weights, balances, and fees of this pool are immutable. In the finalized state, SWAP, JOIN, and EXIT are public. CONTROL capabilities are disabled.

Trading and Liquidity Functions


    address tokenIn,
    uint tokenAmountIn,
    address tokenOut,
    uint minAmountOut,
    uint maxPrice
    returns (uint tokenAmountOut, uint spotPriceAfter)

Trades an exact tokenAmountIn of tokenIn taken from the caller by the pool, in exchange for at least minAmountOut of tokenOut given to the caller from the pool, with a maximum marginal price of maxPrice.

Returns (tokenAmountOut, spotPriceAfter), where tokenAmountOut is the amount of token that came out of the pool, and spotPriceAfter is the new marginal spot price, ie, the result of getSpotPrice after the call. (These values are what are limited by the arguments; you are guaranteed tokenAmountOut >= minAmountOut and spotPriceAfter <= maxPrice).


    address tokenIn,
    uint maxAmountIn,
    address tokenOut,
    uint tokenAmountOut,
    uint maxPrice
    returns (uint tokenAmountIn, uint spotPriceAfter)


joinPool(uint poolAmountOut, uint[] calldata maxAmountsIn)

Join the pool, getting poolAmountOut pool tokens. This will pull some of each of the currently trading tokens in the pool, meaning you must have called approve for each token for this pool. These values are limited by the array of maxAmountsIn in the order of the pool tokens.

If the balances you are adding are 10% of the current pool balances, then you should set poolAmountOut as 10% of the current poolSupply. Bear in mind that the proportions of the different underlying token balances might change until your transaction gets mined: therefore you should have a buffer to avoid the transaction being reverted. We usually suggest 1% if you use high gas prices for fast confirmation. So calculate poolAmountOut as described above with 99% of the maxAmountsIn.


exitPool(uint poolAmountIn, uint[] calldata minAmountsOut)

Exit the pool, paying poolAmountIn pool tokens and getting some of each of the currently trading tokens in return. These values are limited by the array of minAmountsOut in the order of the pool tokens.

To define minAmountsOut, consider the percentage of the pool liquidity you are withdrawing, which is poolAmountIn/poolSupply and multiply that percentage by each of the underlying pool token balances. If you expect to receive say 10 units of each of the underlying tokens in the pool, consider setting minAmountsOut as 9.9 to allow for variations in the balances proportions that may happen before your transaction gets mined.


joinswapExternAmountIn(address tokenIn, uint tokenAmountIn, uint minPoolAmountOut) -> (uint poolAmountOut)

Pay tokenAmountIn of token tokenIn to join the pool, getting poolAmountOut of the pool shares.


exitswapExternAmountOut(address tokenOut, uint tokenAmountOut, uint maxPoolAmountIn) -> (uint poolAmountIn)

Specify tokenAmountOut of token tokenOut that you want to get out of the pool. This costs poolAmountIn pool shares (these went into the pool).


joinswapPoolAmountOut(address tokenIn, uint poolAmountOut, uint maxAmountIn) -> (uint tokenAmountIn)

Specify poolAmountOut pool shares that you want to get, and a token tokenIn to pay with. This costs tokenAmountIn tokens (these went into the pool).


exitswapPoolAmountIn(address tokenOut, uint poolAmountIn, uint minAmountOut) -> (uint tokenAmountOut)

Pay poolAmountIn pool shares into the pool, getting tokenAmountOut of the given token tokenOut out of the pool.

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