tools-only 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
- Understand which ARC applies to your use case
- Implement the contract following ARC conventions
- Generate application specification files
- 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