01 — Hello Contract

The simplest possible Covenant contract — a greeting stored on-chain and exposed as a read action.

contract HelloWorld {
  /// Greeting stored on chain.
  field greeting: String = "hello, world"

  /// Read the greeting.
  action greet() -> String {
    return self.greeting;
  }

  /// Update the greeting (owner only).
  action set_greeting(msg: String) {
    only(owner);
    self.greeting = msg;
  }
}

What just happened?

Concept	Explanation
`contract`	Top-level declaration; compiles to a single EVM account
`field`	Persistent storage slot — initialised with the literal after `=`
`action`	Public entry point, maps to an ABI function
`only(owner)`	Built-in guard: reverts unless `msg.sender == owner()`

Build it

covenant new hello-world
cd hello-world
# Replace src/main.cov with the snippet above
covenant build      # emits hello-world.abi + hello-world.bin
covenant test       # runs the snapshot test suite

Deploy to a local devnet

covenant devnet &           # starts Anvil-compatible devnet
covenant deploy --dev       # deploys to 0x0…01 with test key

The CLI prints the deployed address. Continue to 02 — Fields & Storage to learn about all storage types.