Building a World

A World is the abstraction that allows workflows to run on any infrastructure. It handles workflow storage, step execution queuing, and data streaming. This guide explains the World interface and how to implement your own.

What is a World?

A World connects workflows to the infrastructure that powers them. The World interface abstracts three core responsibilities:

1. Storage — Persisting workflow runs, steps, hooks, and the event log
2. Queue — Enqueuing and processing workflow and step invocations
3. Streamer — Managing real-time data streams between workflows and clients

interface World extends Storage, Queue, Streamer {
  start?(): Promise<void>;
}

The optional start() method initializes any background tasks needed by your World (e.g., queue polling).

The Event Log Model

Workflow storage is built on an append-only event log. All state changes happen through events — you never modify runs, steps, or hooks directly. Instead, you create events that update the materialized state.

Events fall into three categories: run lifecycle events, step lifecycle events, and hook lifecycle events. See the Event Sourcing documentation for a complete list of event types and their semantics.

Storage Interface

The Storage interface provides read access to materialized entities and write access through events:

interface Storage {
  runs: {
    get(id: string, params?: GetWorkflowRunParams): Promise<WorkflowRun>;
    list(params?: ListWorkflowRunsParams): Promise<PaginatedResponse<WorkflowRun>>;
  };

  steps: {
    get(runId: string | undefined, stepId: string, params?: GetStepParams): Promise<Step>;
    list(params: ListWorkflowRunStepsParams): Promise<PaginatedResponse<Step>>;
  };

  events: {
    // Create a new workflow run (runId must be null - server generates it)
    create(runId: null, data: RunCreatedEventRequest, params?: CreateEventParams): Promise<EventResult>;
    
    // Create an event for an existing run
    create(runId: string, data: CreateEventRequest, params?: CreateEventParams): Promise<EventResult>;
    
    list(params: ListEventsParams): Promise<PaginatedResponse<Event>>;
    listByCorrelationId(params: ListEventsByCorrelationIdParams): Promise<PaginatedResponse<Event>>;
  };

  hooks: {
    get(hookId: string, params?: GetHookParams): Promise<Hook>;
    getByToken(token: string, params?: GetHookParams): Promise<Hook>;
    list(params: ListHooksParams): Promise<PaginatedResponse<Hook>>;
  };
}

Key Implementation Details

Event Creation: When events.create() is called, your implementation must:

1. Persist the event to the event log
2. Atomically update the affected entity (run, step, or hook)
3. Return both the created event and the updated entity

Run Creation: For run_created events, the runId parameter is null. Your World generates and returns a new runId.

Hook Tokens: Hook tokens must be unique. If a hook_created event conflicts with an existing token, return a hook_conflict event instead.

Automatic Hook Disposal: When a workflow reaches a terminal state (completed, failed, or cancelled), automatically dispose of all associated hooks to release tokens for reuse.

Queue Interface

The Queue interface handles asynchronous execution of workflows and steps:

interface Queue {
  getDeploymentId(): Promise<string>;

  queue(
    queueName: ValidQueueName,
    message: QueuePayload,
    opts?: QueueOptions
  ): Promise<{ messageId: MessageId }>;

  createQueueHandler(
    queueNamePrefix: QueuePrefix,
    handler: (message: unknown, meta: { attempt: number; queueName: ValidQueueName; messageId: MessageId }) => Promise<void | { timeoutSeconds: number }>
  ): (req: Request) => Promise<Response>;
}

Queue Names

Queue names follow a specific pattern:

• __wkf_workflow_<name> — For workflow invocations
• __wkf_step_<name> — For step invocations

Message Payloads

Two types of messages flow through queues:

Workflow Invocations:

interface WorkflowInvokePayload {
  runId: string;
  traceCarrier?: Record<string, string>;  // OpenTelemetry context
  requestedAt?: Date;
}

Step Invocations:

interface StepInvokePayload {
  workflowName: string;
  workflowRunId: string;
  workflowStartedAt: number;
  stepId: string;
  traceCarrier?: Record<string, string>;
  requestedAt?: Date;
}

Implementation Considerations

• Messages must be delivered at-least-once
• Support configurable retry policies
• Track attempt counts for observability
• Implement idempotency using the idempotencyKey option when provided

Streamer Interface

The Streamer interface enables real-time data streaming:

interface Streamer {
  writeToStream(
    name: string,
    runId: string | Promise<string>,
    chunk: string | Uint8Array
  ): Promise<void>;

  closeStream(
    name: string,
    runId: string | Promise<string>
  ): Promise<void>;

  readFromStream(
    name: string,
    startIndex?: number
  ): Promise<ReadableStream<Uint8Array>>;

  listStreamsByRunId(runId: string): Promise<string[]>;
}

Streams are identified by a combination of runId and name. Each workflow run can have multiple named streams.

Reference Implementations

Study these implementations for guidance:

• Local World — Filesystem-based, great for understanding the basics
• Postgres World — Database-backed with pg-boss for queuing

Testing Your World

Workflow DevKit includes an E2E test suite that validates World implementations. Once your World is published to npm:

1. Add your world to worlds-manifest.json
2. Open a PR to the Workflow repository
3. CI will automatically run the E2E test suite against your implementation

Your world will then appear on the Worlds Ecosystem page with its compatibility status and performance benchmarks.

Publishing Your World

1. Package your World — Export a default World instance from your package
2. Publish to npm — Publish your package to npm
3. Add to the manifest — Submit a PR adding your world to worlds-manifest.json
4. Document configuration — Clearly document any required environment variables

// worlds-manifest.json entry
{
  "package": "your-world-package",
  "repository": "https://github.com/you/your-world",
  "docs": "https://github.com/you/your-world#readme"
}