01 — Hello Contract

The minimal viable Covenant file: a record with one field, one setter action, and one read view. This is the canonical starting point.

-- Hello.cov · the minimal viable Covenant file.
-- A `record` is a key-value store on chain: fields + actions + views,
-- nothing else. The simplest building block in the language.

record Hello {
    greeting: text

    action update(new_text: text) {
        greeting = new_text
    }

    view read returns text {
        greeting
    }
}

What just happened?

Concept	Explanation
`--`	Single-line comment (Covenant uses Haskell-style, not `//`)
`record`	Top-level keyword: a key-value store on chain
`greeting: text`	Field declaration; `text` is the UTF-8 string type. Inside `record` the `field` keyword is implicit
`action update(...)`	State-mutating function. Default visibility is external — no `public`/`external` modifier needed
`view read returns text`	Read-only query. Zero-arg views drop the parentheses — write `view read returns text`, not `view read() returns text`
(no `return` keyword in body)	Single-expression view bodies are expression-bodied: the last expression is the return value

Try it now — no install required

Try in Playground →

The button opens the Covenant Playground with this contract pre-loaded. From there:

Compile — the Inspector panel shows real EVM bytecode + ABI
Deploy (target: MockChain) — the contract gets a deterministic address in ~50ms
In Interaction Panel, find update, type a string, click Call
Find read, click Query — returns what you just set

Switch the Chain Target to Sepolia to deploy to a real testnet via MetaMask (~30s with confirmation).

Build it locally (CLI)

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

Continue

Move on to 02 — Fields & Storage to see how to declare more complex state.