designing-entities

Designing entities

Guided, 5-phase workflow for designing and implementing one Electric Agents entity. Infers the coordination pattern from the user's description, reviews the design against universal and pattern-specific checks, and writes a single entity file once approved.

When to use

• User is starting a new entity in their app (registry.define(...) / registerXxx(registry)).
• User asks "how do I build an agent that..." / "I want an entity that...".

Do not use when editing an existing entity, querying entity streams (see the entity-stream-queries skill), or changing the runtime itself.

Workflow

The five phases are strict — do not skip, merge, or reorder. Reference files are loaded on demand only when the phase below says so.

1. Elicit

Ask the developer one open question:

Describe the entity you want to build. What should it do? Who/what does it interact with? What triggers it?

Skip this prompt if the opening message already contains a clear description.

2. Clarify

Load references/pattern-triggers.md. Match the description against the trigger table. If one pattern fits clearly, skip ahead. Otherwise, ask one disambiguation question per message — focused on narrowing the coordination shape (spawns / parallel vs sequential / fixed vs dynamic specialists / shared state / observes / LLM vs orchestration-only). Stop as soon as the pattern and shape are unambiguous. Typical count: 2–4 questions. Never ask a canned full list.

3. Propose pattern and design

State the inferred pattern and the reasoning:

Inferred pattern: <name>
Why: <trigger phrases> + <structural signals>

Load references/patterns/<selected>.md. If runtime details are needed, read the authoritative docs on demand (see "Canonical material" below). Then present the design outline in chat:

• Entity type name + description
• Coordination pattern (or "single-agent — no coordination")
• creationSchema (if spawn args are expected) — field names + types
• state collections — names, primary keys, row shape
• inboxSchemas (if messages are typed)
• stateSchemas (if the entity produces typed state events)
• Handler outline — firstWake init, wake-type branches, agent config, spawn/observe calls
  • Key ctx properties: ctx.db.actions.* (insert/update/delete), ctx.db.collections.* (get/toArray), ctx.tags / ctx.setTag(key, value) / ctx.deleteTag(key), ctx.events (Array of ChangeEvent from observed sources)
  • Observation sources: entity(url), cron(expression), entities({ tags: ... }) — import from @electric-ax/agents-runtime
  • ctx.send(url, payload, { type?, afterMs? }) — afterMs delays delivery
• Built-in agents referenced (e.g. worker), if any
• registerXxx(registry) factory wrapping it

Ask: "Design look right? Any changes before we run the review checks?" Wait for the answer. Revise if requested, then re-present the outline.

4. Review (loop until approved)

Load references/review-checklist.md. The pattern file from step 3 is already loaded. Apply both checklists mechanically against the design. Report:

Universal checks:
  ✓ Handler signature correct
  ✓ ...ctx.electricTools spread into tools array
  ✗ Spawn-once guard missing — child IDs collide on re-wake
  N/A creationSchema — no spawn args

Pattern-specific (<name>):
  ✗ State machine transitions not defined
  ✓ Parallel spawn loop uses deterministic IDs

Proposed fixes:
  - Add state.children collection + spawn-once guard
  - Add state.status with transitions idle → mapping → reducing → idle

Apply these fixes? Anything to override?

Iterate: developer requests changes → revise design → re-run both checklists → report again. Loop until the developer explicitly approves ("looks good, write the file" or equivalent).

5. Implement

Confirm the output path — default entities/<type-name>.ts, or whatever the developer specifies. Write exactly one file using this shape:

import type { EntityRegistry } from "@electric-ax/agents-runtime"
import { z } from "zod/v4"

// schemas (creationSchema, inboxSchemas, collection schemas) go here

export function register<Name>(registry: EntityRegistry) {
  registry.define("<type>", {
    description: "...",
    creationSchema,
    inboxSchemas,
    state: { ... },
    async handler(ctx, wake) { ... },
  })
}

After writing, tell the developer:

Wire it in by adding register<Name>(registry) to your registry composition file (typically entities/registry.ts or server.ts).

Do not patch the developer's registry file automatically. Stop — skill is done.

Invariants

• One question per message in phase 2.
• No files written before phase 5.
• Phase 4 loops until the developer explicitly approves.
• Reference files are loaded on demand, never upfront.
• The skill writes exactly one entity file. Multi-entity systems are designed by running the skill once per entity.

Canonical material (read on demand, do not preload)

How to access docs: paths below are relative routes (e.g. /docs/reference/handler-context). If the file is available locally at electric-agents-docs/docs/, read it from disk. Otherwise fetch from https://durable-agents-docs.netlify.app/ + the route (e.g. https://durable-agents-docs.netlify.app/docs/reference/handler-context).

Runtime API reference:

• /docs/reference/handler-context — the ctx API (db, state, spawn, observe, send, agent, electricTools, firstWake, sleep, tags, setTag, deleteTag, events).
• /docs/reference/wake-event — wake event types and the Wake configuration object.
• /docs/reference/entity-definition — full EntityDefinition interface.
• /docs/reference/built-in-collections — the 17 built-in collections on db.collections.*.
• /docs/reference/state-collection-proxy — ctx.db.actions.* (insert/update/delete) and ctx.db.collections.* (get/toArray) API.
• /docs/reference/shared-state-handle — mkdb / observe(db(...)).
• /docs/reference/agent-config — useAgent, AgentHandle.run(), testResponses.
• /docs/reference/agent-tool — custom tool interface.
• /docs/reference/entity-handle — what ctx.spawn / ctx.observe return.

Usage guides:

• /docs/usage/writing-handlers — handler lifecycle and re-entrancy.
• /docs/usage/waking-entities — how wakes are produced and consumed; authoritative mental model for wake.type (only "inbox" and "wake").
• /docs/usage/defining-entities — registry and collection declaration patterns.

Built-in agent types:

• /docs/entities/agents/horton — the dev-server's built-in assistant (chat, research, code, dispatch). Useful as a reference for custom single-agent entities.
• /docs/entities/agents/worker — the built-in sandboxed subagent. Required spawn args: { systemPrompt, tools } where tools is a non-empty subset of WorkerToolName. Workers do not receive ctx.electricTools (least-privilege).

Pattern descriptions:

• /docs/entities/patterns/<name> — one per pattern.

Canonical example implementations:

• examples/durable-agents-playground/src/coordination/{manager-worker,pipeline,map-reduce,dispatcher}.ts
• examples/durable-agents-playground/src/blackboard/{debate,wiki,peer-review,trading-floor}.ts
• examples/durable-agents-playground/src/reactive/{monitor,summarizer,guardian}.ts
• examples/durable-agents-playground/src/standalone/assistant.ts
• examples/durable-agents-playground/src/workers/worker.ts — the playground registers its own worker type that accepts sharedState / builtinTools. When a real app spawns "worker" it gets the server's built-in least-privilege worker instead; adjust pattern examples accordingly.

Each references/patterns/<name>.md points at the specific canonical example for that pattern.