# Add `read-only` annotation to ABI methods

The following document introduces a convention for creating methods (as described in [ARC-4](https://dev.algorand.co/arc-standards/arc-0004)) which don’t mutate state.

## Abstract

The goal of this convention is to allow smart contract developers to distinguish between methods which mutate state and methods which don’t by introducing a new property to the `Method` descriptor.

## Specification

The key words “ **MUST**”, “ **MUST NOT**”, “ **REQUIRED**”, “ **SHALL**”, “ **SHALL NOT**”, “ **SHOULD**”, “ **SHOULD NOT**”, “ **RECOMMENDED**”, “ **MAY**”, and “ **OPTIONAL**” in this document are to be interpreted as described in [RFC-2119](https://www.ietf.org/rfc/rfc2119.txt).

> Comments like this are non-normative.

### Read-only functions

A `read-only` function is a function with no side-effects. In particular, a `read-only` function **SHOULD NOT** include:

- local/global state modifications
- calls to non `read-only` functions
- inner-transactions

It is **RECOMMENDED** for a `read-only` function to not access transactions in a group or metadata of the group.

> The goal is to allow algod to easily execute `read-only` functions without broadcasting a transaction

In order to support this annotation, the following `Method` descriptor is suggested:

```
interface Method {

/** The name of the method */

name: string;

/** Optional, user-friendly description for the method */

desc?: string;

/** Optional, is it a read-only method (according to ARC-22) */

readonly?: boolean

/** The arguments of the method, in order */

args: Array<{

/** The type of the argument */

type: string;

/** Optional, user-friendly name for the argument */

name?: string;

/** Optional, user-friendly description for the argument */

desc?: string;

}>;

/** Information about the method's return value */

returns: {

/** The type of the return value, or "void" to indicate no return value. */

type: string;

/** Optional, user-friendly description for the return value */

desc?: string;

};

}
```

## Rationale

## Security Considerations

None.

## Copyright

Copyright and related rights waived via [CCO](https://creativecommons.org/publicdomain/zero/1.0/).