Run Your First Slice

This walkthrough shows a slice going from Planned on your Eventmodelers board to a tested, working Cratis vertical slice in your Kotlin project — with no manual coding in between.

Prerequisites

Install the kit and connect it to a board first. The loop needs a running agent (node .build-kit/ralph-claude.js) and valid credentials in .eventmodelers/config.json.

Look at the example slice first

Every install ships a working example under SomeModule/SomeFeature/ — a Registration slice (a command and its event) and a Listing slice (a projection and read model). Open them before you build your own; they show every convention the kit’s build skills reproduce:

• One file per slice, with the command/event/reactor together
• @Command/@EventType-style artifacts with a handle()-shaped method that returns the event
• The React screen and command wiring in .tsx/.ts files beside them

Start the loop

node .build-kit/ralph-claude.js

The loop polls for two independent triggers — see Understanding the Loop — and idles quietly until one fires.

1. Mark a slice Planned on your board

On app.eventmodelers.ai, create or open a slice and set its status to Planned. For example, a “Register Author” slice might look like:

{
  "id": "slice-123",
  "title": "Register Author",
  "status": "Planned",
  "contextName": "Authors",
  "sliceType": "StateChange",
  "commands": ["RegisterAuthor"],
  "events": ["AuthorRegistered"],
  "description": "Register a new author with name and email"
}

2. The kit fetches and persists the slice

The real-time subscription picks up the status change and saves the definition to .build-kit/.slices/Authors/register-author/slice.json.

3. The kit generates the vertical slice

Because the slice only carries commands/events (no processors, no projections/queries), the loop routes to the build-state-change skill, which generates Authors/Registration/Registration.kt:

@Command
@AllowAnonymous
data class RegisterAuthor(
    @CommandKey val id: String,
    val name: String
) {
    fun handle(): AuthorRegistered = AuthorRegistered(AuthorName(name))
}

@EventType
data class AuthorRegistered(val name: AuthorName)

4. The kit builds and tests the slice

./gradlew build
./gradlew test

5. The kit updates the board to Done

Once the build and tests pass, the kit calls back to the platform and marks the slice Done — closing the loop without you touching an editor.

What’s next

• Try a slice with projections/readModel set — it routes to build-state-view instead
• Try a slice with processors set — it routes to build-automation
• If a slice gets stuck in InProgress, check the loop’s terminal output, confirm ./gradlew build succeeds locally, then re-run the loop