diff --git a/eth_interface.md b/eth_interface.md
index ceeee749..da95b951 100644
--- a/eth_interface.md
+++ b/eth_interface.md
@@ -15,6 +15,9 @@ We also define the following WebAssembly data types:
 - `i32ptr`: same as `i32` in WebAssembly, but treated as a pointer to a WebAssembly memory offset
 - `i64`: same as `i64` in WebAssembly
 
+# Tables
+A table named 'callback' must be exported if any callbacks are used. All callbacks functions have a parameter of a single `i32` which will contain the error code of the orginal operation. If there where no errors then the return value will be 0 other wise it will be 1.
+
 # API
 
 ## useGas
@@ -51,6 +54,7 @@ offset.
 
 -   `addressOffset` **i32ptr** the memory offset to load the address from (`address`)
 -   `resultOffset` **i32ptr** the memory offset to load the balance into (`u128`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
@@ -82,10 +86,11 @@ Sends a message with arbitrary date to a given address path
 -   `dataLength` **i32** the length of data
 -   `resultOffset` **i32ptr** the memory offset to store the result data at (`bytes`)
 -   `resultLength` **i32** the maximal length of result data
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`result` **i32** Returns 1 or 0 depending on if the VM trapped on the message or not
+*nothing*
 
 ## callDataCopy
 
@@ -128,10 +133,11 @@ data passed with the message call instruction or transaction.
 -   `dataLength` **i32** the length of data
 -   `resultOffset` **i32ptr** the memory offset to store the result data at (`bytes`)
 -   `resultLength` **i32** the maximal length of result data
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`result` **i32** Returns 1 or 0 depending on if the VM trapped on the message or not
+*nothing*
 
 ## callDelegate
 
@@ -146,10 +152,11 @@ persisting the current values for sender and value.
 -   `dataLength` **i32** the length of data
 -   `resultOffset` **i32ptr** the memory offset to store the result data at (`bytes`)
 -   `resultLength` **i32** the maximal length of result data
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`result` **i32** Returns 1 or 0 depending on if the VM trapped on the message or not
+*nothing*
 
 ## storageStore
 
@@ -159,6 +166,7 @@ Store 256-bit a value in memory to persistent storage
 
 -   `pathOffest` **i32ptr** the memory offset to load the path from (`u256`)
 -   `valueOffset` **i32ptr** the memory offset to load the value from (`u256`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
@@ -172,6 +180,7 @@ Loads a 256-bit a value to memory from persistent storage
 
 -   `pathOffest` **i32ptr** the memory offset to load the path from (`u256`)
 -   `resultOffset` **i32ptr** the memory offset to store the result at (`u256`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
@@ -223,11 +232,12 @@ Gets the size of code running in current environment.
 
 **Parameters**
 
-*none*
+-   `resultOffset` **i32ptr** the memory offset to load the result into (`i32`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`codeSize` **i32**
+*nothing*
 
 ## getBlockCoinbase
 
@@ -251,10 +261,11 @@ Creates a new contract with a given value.
 -   `dataOffset` **i32ptr** the memory offset to load the code for the new contract from (`bytes`)
 -   `length` **i32** the data length
 -   `resultOffset` **i32ptr** the memory offset to write the new contract address to (`address`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`result` **i32** Returns 1 or 0 depending on if the VM trapped on the message or not
+*nothing*
 
 ## getBlockDifficulty
 
@@ -278,6 +289,7 @@ Copies the code of an account to memory.
 -   `resultOffset` **i32ptr** the memory offset to load the result into (`bytes`)
 -   `codeOffset` **i32** the offset within the code
 -   `length` **i32** the length of code to copy
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
@@ -290,10 +302,12 @@ Get size of an account’s code.
 **Parameters**
 
 -   `addressOffset` **i32ptr** the memory offset to load the address from (`address`)
+-   `resultOffset` **i32ptr** the memory offset to load the result into (`i32`)
+-   `callBackIndex` **i32** an index of the callback function
 
 **Returns**
 
-`extCodeSize` **i32**
+*nothing*
 
 ## getGasLeft