Homerun

Typed, testable Home Assistant automations in TypeScript.

Status: pre-1.0. The API may change. Builds are published to npm as @ajclarkson/homerun (edge tag, on every push to main) and as a Docker image, ghcr.io/ajclarkson/homerun:edge.

Homerun is a framework that replaces HA automations and Node-RED flows with pure functions. Every automation is a context builder and a reducer — no side effects, no hidden state, no YAML. The pipeline handles observability, error isolation, and action execution.

---

The problem

Home Assistant automations are YAML. Node-RED flows are JSON blobs. Both are hard to test, hard to review, and impossible to type-check. A bad deploy silently breaks your lights at 2am.

Homerun brings the same discipline you'd apply to application code: pure functions, typed inputs, and a test suite that runs in milliseconds.

---

How it works

Every automation follows the same pipeline:

Event → context() → reduce() → actions[]

context() reads from the HA state cache and returns a typed snapshot — or aborts early if a required input is missing. It is the only place that touches external state.

reduce() is a pure function. It receives the context and returns a decision with a list of declarative actions. No async, no side effects, no HA calls.

The pipeline handles everything else: correlation IDs, observability events, error isolation, and action execution.

---

Example

import { defineAutomation, abort, requireState, requireNumericState } from '@ajclarkson/homerun';

export default defineAutomation({
  id: 'kitchen:lighting',
  location: 'kitchen',
  subsystem: 'lighting',

  triggers: [
    { type: 'state_changed', entity: 'binary_sensor.kitchen_motion' },
    { type: 'on_start' },
  ],

  context(state) {
    if (requireState(state, 'input_boolean.kitchen_lights_enabled') !== 'on') {
      return abort('automation_disabled');
    }
    return {
      motion: requireState(state, 'binary_sensor.kitchen_motion') === 'on',
      lux: requireNumericState(state, 'sensor.kitchen_lux'),
      luxThreshold: requireNumericState(state, 'input_number.kitchen_lux_threshold'),
    };
  },

  reduce(ctx) {
    const shouldLight = ctx.motion && ctx.lux < ctx.luxThreshold;
    return {
      decision: shouldLight ? 'lights_on' : 'lights_off',
      actions: [
        {
          type: 'ha.call_service',
          domain: 'light',
          service: shouldLight ? 'turn_on' : 'turn_off',
          target: { entity_id: 'light.kitchen_ceiling' },
        },
      ],
    };
  },
});

requireState and requireNumericState abort the run, with the missing entity recorded, if an entity is unavailable or non-numeric, so a dead sensor never silently becomes a wrong decision. The decision's conditions default to the full context, so the published event explains itself.

Files like this go in your automations directory; see Consumer setup.

---

Testing

Because reduce() is a pure function, tests are just function calls. To test the whole automation without a Home Assistant connection, use the test helpers:

import { describe, it, expect } from 'vitest';
import { testAutomation } from '@ajclarkson/homerun/testing';
import kitchenLights from './kitchen-lights';

describe('kitchen lighting', () => {
  it('turns lights on when motion is detected below the lux threshold', () => {
    const result = testAutomation(kitchenLights, {
      event: { type: 'state_changed', entity_id: 'binary_sensor.kitchen_motion', new_state: { state: 'on' } },
      state: {
        'input_boolean.kitchen_lights_enabled': { state: 'on' },
        'binary_sensor.kitchen_motion': { state: 'on' },
        'sensor.kitchen_lux': { state: '20' },
        'input_number.kitchen_lux_threshold': { state: '40' },
      },
    });
    expect(result.decision).toBe('lights_on');
    expect(result.actions[0]).toMatchObject({ service: 'turn_on' });
  });
});

No mocking, no HA connection, no async. testAbort and testUnavailable cover the abort paths. See Automation API.

---

Triggers and actions

Trigger	Fires when
state_changed	An entity's state or attributes change. Filter with to; delay with duration.
schedule	A cron expression fires.
on_start	The system is ready and the state cache is fully populated.
timer_expired	A named timer set by a previous timer.start action expires.
button	A button entity emits a single_press, double_press, or hold gesture.
mqtt_in	A message arrives on a subscribed MQTT topic.

Action	Effect
ha.call_service	Calls a Home Assistant service
mqtt.publish	Publishes to an MQTT topic
timer.start	Starts (or restarts) a named timer
timer.cancel	Cancels a named timer

Actions are returned from reduce() as a plain array; the runtime executes them after the decision event is published. Full types and semantics: Automation API.

---

Observability

Every pipeline run publishes an event to MQTT — whether it decided, aborted, or threw — and every action publishes its own start and result events. A correlation_id minted at the event source lets you trace a HA state change through to the service call that resulted from it.

{
  "schema": "home.events.v2",
  "correlation_id": "b3d2f1a0-...",
  "root_correlation_id": "b3d2f1a0-...",
  "automation_id": "kitchen:lighting",
  "location": "kitchen",
  "subsystem": "lighting",
  "event_type": "decision",
  "trigger": { "type": "state_changed", "entity_id": "binary_sensor.kitchen_motion", "to": "on" },
  "decision": "lights_on",
  "conditions": { "motion": true, "lux": 20, "luxThreshold": 40 },
  "actions": [{ "type": "ha.call_service", "domain": "light", "service": "turn_on" }],
  "hasAction": true,
  "timestamp": "2026-06-23T18:00:00.000Z"
}

Schema, topics, command-ack tracking and Prometheus metrics: Observability.

---

Declared reasons, catalogue and history

By default a decision's reason is a free string. An automation can instead declare the reasons it may give, so a consumer (a dashboard, a notifier) can explain what happened without parsing strings. Everything here is opt-in: an automation without reasons behaves and publishes exactly as before.

export default defineAutomation({
  id: 'kitchen:lighting',
  location: 'kitchen',
  subsystem: 'lighting',
  triggers: [{ type: 'state_changed', entity: 'binary_sensor.kitchen_motion' }],
  reasons: {
    lights_on: { outcome: 'acted' },
    lux_high: { outcome: 'declined', facts: ['lux', 'threshold'] },
    startup: { outcome: 'ignored' },
  },
  context: (state) => ({ lux: requireNumericState(state, 'sensor.kitchen_lux') }),
  reduce: ({ lux }) =>
    lux > 40
      ? { decision: 'no_action', reason: 'lux_high', facts: { lux, threshold: 40 }, actions: [] }
      : { decision: 'turn_on', reason: 'lights_on', actions: [kitchenLightsOn] },
});

• outcome is acted (the rule changed something), declined (it chose not to act and a person would want to know why) or ignored (noise: startup, already in the right state). It is declared, never inferred from actions.
• facts are the typed values a sentence needs: at most 8 keys per reason, each a string, finite number, boolean or null. They are separate from conditions on purpose: conditions is a debug dump of the whole context that may change shape freely, facts is the small, named, checked set a consumer can depend on.
• Declared reasons are enforced three times. At compile time reason is the union of declared keys and facts must carry exactly that reason's keys (an extra key is only caught at run time, as TypeScript does not check excess properties on returned objects). At load time defineAutomation throws on a bad outcome, fact list or reason name (letters, digits and underscores only: reasons carry no free text). At run time an undeclared reason, or an undeclared, missing or non-primitive fact, never stops the actions: the decision is published without outcome or facts (the undeclared shape) and a separate declaration_error event is published to homerun/events and logged, with problem (undeclared_reason, missing_fact, undeclared_fact or invalid_fact_value) and, when identifier-shaped, reason and fact. Observability must never prevent a real action. Automations that declare nothing cannot return facts (a compile error). defineAutomation and the registry (including hot reload) both reject a bad declaration, and the reserved location dev, at load.
• The decision event gains optional outcome and facts, only for declaring automations.

Catalogue. The declarations are published retained on homerun/catalog (home.catalog.v1) at startup and after a reload, and each entry's reasons is added to GET /automations. Only automations that declare reasons appear. The catalogue is published on every startup, empty if nothing declares reasons, so a retained copy is never stale. A consumer can check its wording table against it.

History. Set history in the configuration (off by default) to keep a ring buffer of the events worth asking "what happened here?" about:

history:
  size: 20        # per location, 1 to 200
  houseSize: 30   # house-wide, 1 to 200

Each stored entry is republished, newest first, retained on homerun/{location}/history and homerun/history (home.history.v1). Remembered: declared acted and declined decisions (or, for undeclared automations, decisions with an action), aborts other than disabled, and failed actions (a failed action_result or an action_ack_timeout). Entries are structured only: reason keys, facts, a trigger summary, and a detail record (abort_kind/entity/stage/error_type, or failure/action/entity). Retained republishes are coalesced (250ms) with the latest state always published, and flushed on shutdown. On startup the buffers are re-seeded from the retained topics, so history survives a restart; a malformed retained message is logged and that buffer starts empty. Seeding waits 1s for the broker to deliver the retained messages. dev is reserved as a location name (rejected at registration). Both the catalogue and history follow events.enabled: when it is false, neither is published (nor history seeded or kept), like the rest of the MQTT stream. In dry-run mode every one of these topics moves under homerun/dev/.

The JSON Schemas for both payloads are in schemas/ and published with the package. Every payload is validated against them before it is published.

---

Running

npm install @ajclarkson/homerun

Homerun reads a configuration.yaml (path from HOMERUN_CONFIG) with your Home Assistant URL and token, MQTT broker and automations directory. Secrets can live in a secrets.yaml beside it and be referenced with !secret. configuration.yaml.example shows every option.

Set options.dry_run: true to run the full pipeline — context, reduce, observability — without executing any actions.

Setting up your own automations repo, generating entity types from your Home Assistant, and running the runtime are covered in Consumer setup.

To work on the framework itself, clone this repo and use npm run dev (run from source, hot-reloads) and npm test.

---

HTTP API

The server exposes an HTTP API on port 7070 by default (server.port in the config).

Method	Path	Description
GET	/health/live	Always returns 200 { status: "live" } — used for liveness probes.
GET	/health/ready	Returns 200 when the HA state cache is populated and automations are loaded, 503 while starting. Response includes entities, automations counts, and dry_run: true if running in dry-run mode.
GET	/automations	Lists all registered automations with their id, location, subsystem, and trigger types, plus reasons for those that declare them.
POST	/automations/:id/trigger	Manually fires an on_start event for the given automation.
POST	/reload	Rescans the automations directory and hot-reloads changed files.
GET	/events	Server-sent event stream of all pipeline decisions and action events in real time.

---

Architecture

HAClient ──────────────────────────────────────┐
  └─ state_changed (per entity, with corr. ID) │
                                               ▼
Scheduler (cron / on_start) ──────► TriggerEngine.dispatch()
TimerManager (setTimeout)  ──────►        │
                                          ▼
                                   matchAndFire()
                                          │
                              ┌───────────▼──────────┐
                              │    Pipeline Runner    │
                              │  context → reduce     │
                              │  → validate → fanout  │
                              └──────────┬────────────┘
                                         │
                          ┌──────────────┴──────────────┐
                          ▼                             ▼
                   Observability                  ActionRuntime
                 (MQTT events)           (HA calls / timers / MQTT)

---

License

MIT