Implement ARC Standards

ARC (Algorand Request for Comments) standards define conventions for encoding, method calls, and application specifications on Algorand. This skill covers the most essential ARCs for smart contract development.

Overview / Core Workflow

1. Understand which ARC applies to your use case
2. Implement the contract following ARC conventions
3. Generate application specification files
4. Use the app spec to build typed clients

How to proceed

Key ARCs for Smart Contract Development

ARC	Purpose	When to Use
ARC-4	Application Binary Interface (ABI)	All smart contract method calls, type encoding
ARC-22	Read-only method annotation	Methods that don't modify state
ARC-28	Event logging specification	Emitting structured events
ARC-32	Application Specification (deprecated)	Legacy app specs (use ARC-56 instead)
ARC-56	Extended App Description	Modern app specs with full contract metadata

ARC-4: The Foundation

ARC-4 defines how to encode method calls and data types for Algorand smart contracts.

Method Signatures

A method signature uniquely identifies a method: name(arg_types)return_type

# Method signature: add(uint64,uint64)uint128
# Method selector: first 4 bytes of SHA-512/256 hash

from algopy import ARC4Contract, arc4

class Calculator(ARC4Contract):
    @arc4.abimethod
    def add(self, a: arc4.UInt64, b: arc4.UInt64) -> arc4.UInt128:
        return arc4.UInt128(a.native + b.native)

import { Contract } from '@algorandfoundation/algorand-typescript'
import { abimethod, UInt64, UInt128 } from '@algorandfoundation/algorand-typescript/arc4'

class Calculator extends Contract {
  @abimethod()
  add(a: UInt64, b: UInt64): UInt128 {
    return new UInt128(a.native + b.native)
  }
}

Method Selector Calculation

Method signature: add(uint64,uint64)uint128
SHA-512/256 hash: 8aa3b61f0f1965c3a1cbfa91d46b24e54c67270184ff89dc114e877b1753254a
Method selector: 8aa3b61f (first 4 bytes)

ARC-32 vs ARC-56

Feature	ARC-32	ARC-56
State schema	Yes	Yes
Method descriptions	Yes	Yes
Named structs	No	Yes
Default argument values	Partial	Full
Source maps	No	Yes
Events (ARC-28)	No	Yes
Status	Deprecated	Current

Use ARC-56 for new projects. ARC-32 is maintained for backwards compatibility.

Generating App Specs

App specs are automatically generated when compiling with PuyaPy or PuyaTs:

# Generates ContractName.arc32.json and ContractName.arc56.json
algokit project run build

Using App Specs with Clients

// TypeScript with AlgoKit Utils
import { algorandClient } from '@algorandfoundation/algokit-utils'
import appSpec from './Calculator.arc56.json'

const client = algorand.client.getTypedAppClientById(CalculatorClient, {
  appId: 12345n,
  appSpec,
})

const result = await client.send.add({ args: { a: 10n, b: 20n } })

# Python with AlgoKit Utils
from algokit_utils import AlgorandClient
from artifacts.calculator_client import CalculatorClient

algorand = AlgorandClient.default_localnet()
client = algorand.client.get_typed_app_client(
    CalculatorClient,
    app_id=12345,
)

result = client.send.add(a=10, b=20)

Important Rules / Guidelines

Rule	Details
ARC-4 types only in ABI	Use arc4.UInt64, arc4.String, etc. for method arguments and returns
Reference types as arguments only	account, asset, application cannot be return types
15 argument limit	Methods with 16+ args encode extras as a tuple in arg 15
Return prefix	Return values are logged with 151f7c75 prefix
Bare methods have no selector	Bare calls use NumAppArgs == 0 for routing

Common Variations / Edge Cases

Scenario	Approach
Calling ARC-4 method from contract	Use arc4.abi_call() for type-safe inner transactions
Creating contract with method	Use create="require" in @abimethod decorator
Read-only methods (ARC-22)	Use readonly=True parameter in decorator
Emitting events (ARC-28)	Use arc4.emit() with typed event structs

References / Further Reading

• ARC-4 ABI Details - Types, encoding rules, method invocation
• ARC-32/56 App Specs - Application specification details
• ARC Standards - Official ARC documentation
• Call Smart Contracts - Using AlgoKit Utils for ABI calls