ERC-20: Token Standard

Metadata
Status: FinalStandards Track: ERCCreated: 2015-11-19
Authors
Fabian Vogelsteller (fabian@ethereum.org), Vitalik Buterin (vitalik.buterin@ethereum.org)
Links
GitHub page

Simple Summary

A standard interface for tokens.

Abstract

The following standard allows for the implementation of a standard API for tokens within smart contracts. This standard provides basic functionality to transfer tokens, as well as allow tokens to be approved so they can be spent by another on-chain third party.

Motivation

A standard interface allows any tokens on Ethereum to be re-used by other applications: from wallets to decentralized exchanges.

Specification

Token

Methods

NOTES:

  • The following specifications use syntax from Solidity 0.4.17 (or above)
  • Callers MUST handle false from returns (bool success). Callers MUST NOT assume that false is never returned!

name

Returns the name of the token - e.g. "MyToken".

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.



symbol


Returns the symbol of the token. E.g. "HIX".


OPTIONAL - This method can be used to improve usability,
but interfaces and other contracts MUST NOT expect these values to be present.




decimals


Returns the number of decimals the token uses - e.g. 8, means to divide the token amount by 100000000 to get its user representation.


OPTIONAL - This method can be used to improve usability,
but interfaces and other contracts MUST NOT expect these values to be present.




totalSupply


Returns the total token supply.




balanceOf


Returns the account balance of another account with address _owner.




transfer


Transfers _value amount of tokens to address _to, and MUST fire the Transfer event.
The function SHOULD throw if the message caller's account balance does not have enough tokens to spend.


Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.




transferFrom


Transfers _value amount of tokens from address _from to address _to, and MUST fire the Transfer event.


The transferFrom method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf.
This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies.
The function SHOULD throw unless the _from account has deliberately authorized the sender of the message via some mechanism.


Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.




approve


Allows _spender to withdraw from your account multiple times, up to the _value amount. If this function is called again it overwrites the current allowance with _value.


NOTE: To prevent attack vectors like the one described here and discussed here,
clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to 0 before setting it to another value for the same spender.
THOUGH The contract itself shouldn't enforce it, to allow backwards compatibility with contracts deployed before




allowance


Returns the amount which _spender is still allowed to withdraw from _owner.




Events


Transfer


MUST trigger when tokens are transferred, including zero value transfers.


A token contract which creates new tokens SHOULD trigger a Transfer event with the _from address set to 0x0 when tokens are created.




Approval


MUST trigger on any successful call to approve(address _spender, uint256 _value).




Implementation


There are already plenty of ERC20-compliant tokens deployed on the Ethereum network.
Different implementations have been written by various teams that have different trade-offs: from gas saving to improved security.


Example implementations are available at



History


Historical links related to this standard:



Copyright


Copyright and related rights waived via CC0.