Explain an ABI.


JSON String ABI (Solidity Output JSON)

The JSON ABI Format is the format that is output from the Solidity compiler.

A JSON serialized object is always a string, which represents an Array of Objects, where each Object has various properties describing the Fragment of the ABI.

The deserialized JSON string (which is a normal JavaScript Object) may also be passed into any function which accepts a JSON String ABI.

Human-Readable ABI

The Human-Readable ABI was introduced by ethers in this article and has since gained wider adoption.

The ABI is described by using an array of strings, where each string is the Solidity signature of the constructor, function, event or error.

When parsing a fragment, all inferred properties will be injected (e.g. a payable method will have its constant proeprty set to false).

Tuples can be specified by using the tuple(...) syntax or with bare (additional) parenthesis, (...).

Example Human-Readable ABI
const ABI = [ // Constructor "constructor(address ens)", // Constant functions (pure or view) "function balanceOf(address owner) view returns (uint)", // State-mutating functions (payable or non-payable) "function mint(uint amount) payable", "function transfer(address to, uint amount) returns (bool)", // Events "event Transfer(address indexed from, address indexed to, uint amount)", // Errors "error InsufficientFunds(address from, uint balance)", ]

Output Formats

Each Fragment and ParamType may be output using its format method.

ethers.utils.FormatTypes.full string

This is a full human-readable string, including all parameter names, any optional modifiers (e.g. indexed, public, etc) and white-space to aid in human readability.

ethers.utils.FormatTypes.minimal string

This is similar to full, except with no unnecessary whitespace or parameter names. This is useful for storing a minimal string which can still fully reconstruct the original Fragment using Fragment . from.

ethers.utils.FormatTypes.json string

This returns a JavaScript Object which is safe to call JSON.stringify on to create a JSON string.

ethers.utils.FormatTypes.sighash string

This is a minimal output format, which is used by Solidity when computing a signature hash or an event topic hash.


The sighash format is insufficient to re-create the original Fragment, since it discards modifiers such as indexed, anonymous, stateMutability, etc.

It is only useful for computing the selector for a Fragment, and cannot be used to format an Interface.


An ABI is a collection of Fragments, where each fragment specifies:

Properties string

This is the name of the Event or Function. This will be null for a ConstructorFragment.

fragment.type string

This is a string which indicates the type of the Fragment. This will be one of:

  • constructor
  • event
  • function

fragment.inputs Array< ParamType >

This is an array of each ParamType for the input parameters to the Constructor, Event of Function.


fragment.format( [ format = sighash ] ) string

Creates a string representation of the Fragment using the available output formats.

ethers.utils.Fragment.from( objectOrString ) Fragment

Creates a new Fragment sub-class from any compatible objectOrString.

ethers.utils.Fragment.isFragment( object ) boolean

Returns true if object is a Fragment.

ConstructorFragment inherits Fragment


fragment.gas BigNumber

This is the gas limit that should be used during deployment. It may be null.

fragment.payable boolean

This is whether the constructor may receive ether during deployment as an endowment (i.e. msg.value != 0).

fragment.stateMutability string

This is the state mutability of the constructor. It can be any of:

  • nonpayable
  • payable


ethers.utils.ConstructorFragment.from( objectOrString ) ConstructorFragment

Creates a new ConstructorFragment from any compatible objectOrString.

ethers.utils.ConstructorFragment.isConstructorFragment( object ) boolean

Returns true if object is a ConstructorFragment.

ErrorFragment inherits Fragment


ethers.utils.ErrorFragment.from( objectOrString ) ErrorFragment

Creates a new ErrorFragment from any compatible objectOrString.

ethers.utils.ErrorFragment.isErrorFragment( object ) boolean

Returns true if object is an ErrorFragment.

EventFragment inherits Fragment


fragment.anonymous boolean

This is whether the event is anonymous. An anonymous Event does not inject its topic hash as topic0 when creating a log.


ethers.utils.EventFragment.from( objectOrString ) EventFragment

Creates a new EventFragment from any compatible objectOrString.

ethers.utils.EventFragment.isEventFragment( object ) boolean

Returns true if object is an EventFragment.

FunctionFragment inherits ConstructorFragment


fragment.constant boolean

This is whether the function is constant (i.e. does not change state). This is true if the state mutability is pure or view.

fragment.stateMutability string

This is the state mutability of the constructor. It can be any of:

  • nonpayable
  • payable
  • pure
  • view

fragment.outputs Array< ParamType >

A list of the Function output parameters.


ethers.utils.FunctionFragment.from( objectOrString ) FunctionFragment

Creates a new FunctionFragment from any compatible objectOrString.

ethers.utils.FunctionFragment.isFunctionFragment( object ) boolean

Returns true if object is a FunctionFragment.


The following examples will represent the Solidity parameter:

string foobar

Properties string

The local parameter name. This may be null for unnamed parameters. For example, the parameter definition string foobar would be foobar.

paramType.type string

The full type of the parameter, including tuple and array symbols. This may be null for unnamed parameters. For the above example, this would be foobar.

paramType.baseType string

The base type of the parameter. For primitive types (e.g. address, uint256, etc) this is equal to type. For arrays, it will be the string array and for a tuple, it will be the string tuple.

paramType.indexed boolean

Whether the parameter has been marked as indexed. This only applies to parameters which are part of an EventFragment.

paramType.arrayChildren ParamType

The type of children of the array. This is null for any parameter which is not an array.

paramType.arrayLength number

The length of the array, or -1 for dynamic-length arrays. This is null for parameters which are not arrays.

paramType.components Array< ParamType >

The components of a tuple. This is null for non-tuple parameters.


paramType.format( [ outputType = sighash ] )

Creates a string representation of the Fragment using the available output formats.

ethers.utils.ParamType.from( objectOrString ) ParamType

Creates a new ParamType from any compatible objectOrString.

ethers.utils.ParamType.isParamType( object ) boolean

Returns true if object is a ParamType.