TypeBox as protocol source of truth

TypeBox is a TypeScript-first schema library. We use it to define the Gateway WebSocket protocol (handshake, request/response, server events). Those schemas drive runtime validation, JSON Schema export, and Swift codegen for the macOS app. One source of truth; everything else is generated.If you want the higher-level protocol context, start with Gateway architecture.

Mental model (30 seconds)

Every Gateway WS message is one of three frames:

• Request: { type: "req", id, method, params }
• Response: { type: "res", id, ok, payload | error }
• Event: { type: "event", event, payload, seq?, stateVersion? }

The first frame must be a connect request. After that, clients can call methods (e.g. health, send, chat.send) and subscribe to events (e.g. presence, tick, agent).Connection flow (minimal):

Client                    Gateway
  |---- req:connect -------->|
  |<---- res:hello-ok --------|
  |<---- event:tick ----------|
  |---- req:health ---------->|
  |<---- res:health ----------|

Common methods + events:

Authoritative list lives in src/gateway/server.ts (METHODS, EVENTS).

Where the schemas live

• Source: src/gateway/protocol/schema.ts
• Runtime validators (AJV): src/gateway/protocol/index.ts
• Server handshake + method dispatch: src/gateway/server.ts
• Node client: src/gateway/client.ts
• Generated JSON Schema: dist/protocol.schema.json
• Generated Swift models: apps/macos/Sources/MoltbotProtocol/GatewayModels.swift

Current pipeline

• pnpm protocol:gen
  • writes JSON Schema (draft‑07) to dist/protocol.schema.json
• pnpm protocol:gen:swift
  • generates Swift gateway models
• pnpm protocol:check
  • runs both generators and verifies the output is committed

How the schemas are used at runtime

• Server side: every inbound frame is validated with AJV. The handshake only accepts a connect request whose params match ConnectParams.
• Client side: the JS client validates event and response frames before using them.
• Method surface: the Gateway advertises the supported methods and events in hello-ok.

Example frames

Connect (first message):

{
  "type": "req",
  "id": "c1",
  "method": "connect",
  "params": {
    "minProtocol": 2,
    "maxProtocol": 2,
    "client": {
      "id": "moltbot-macos",
      "displayName": "macos",
      "version": "1.0.0",
      "platform": "macos 15.1",
      "mode": "ui",
      "instanceId": "A1B2"
    }
  }
}

Hello-ok response:

{
  "type": "res",
  "id": "c1",
  "ok": true,
  "payload": {
    "type": "hello-ok",
    "protocol": 2,
    "server": { "version": "dev", "connId": "ws-1" },
    "features": { "methods": ["health"], "events": ["tick"] },
    "snapshot": { "presence": [], "health": {}, "stateVersion": { "presence": 0, "health": 0 }, "uptimeMs": 0 },
    "policy": { "maxPayload": 1048576, "maxBufferedBytes": 1048576, "tickIntervalMs": 30000 }
  }
}

Request + response:

{ "type": "req", "id": "r1", "method": "health" }

{ "type": "res", "id": "r1", "ok": true, "payload": { "ok": true } }

Event:

{ "type": "event", "event": "tick", "payload": { "ts": 1730000000 }, "seq": 12 }

Minimal client (Node.js)

Smallest useful flow: connect + health.

import { WebSocket } from "ws";

const ws = new WebSocket("ws://127.0.0.1:18789");

ws.on("open", () => {
  ws.send(JSON.stringify({
    type: "req",
    id: "c1",
    method: "connect",
    params: {
      minProtocol: 3,
      maxProtocol: 3,
      client: {
        id: "cli",
        displayName: "example",
        version: "dev",
        platform: "node",
        mode: "cli"
      }
    }
  }));
});

ws.on("message", (data) => {
  const msg = JSON.parse(String(data));
  if (msg.type === "res" && msg.id === "c1" && msg.ok) {
    ws.send(JSON.stringify({ type: "req", id: "h1", method: "health" }));
  }
  if (msg.type === "res" && msg.id === "h1") {
    console.log("health:", msg.payload);
    ws.close();
  }
});

Worked example: add a method end‑to‑end

Example: add a new system.echo request that returns { ok: true, text }.

1. Schema (source of truth)

Add to src/gateway/protocol/schema.ts:

export const SystemEchoParamsSchema = Type.Object(
  { text: NonEmptyString },
  { additionalProperties: false },
);

export const SystemEchoResultSchema = Type.Object(
  { ok: Type.Boolean(), text: NonEmptyString },
  { additionalProperties: false },
);

Add both to ProtocolSchemas and export types:

  SystemEchoParams: SystemEchoParamsSchema,
  SystemEchoResult: SystemEchoResultSchema,

export type SystemEchoParams = Static<typeof SystemEchoParamsSchema>;
export type SystemEchoResult = Static<typeof SystemEchoResultSchema>;

2. Validation

In src/gateway/protocol/index.ts, export an AJV validator:

export const validateSystemEchoParams =
  ajv.compile<SystemEchoParams>(SystemEchoParamsSchema);

3. Server behavior

Add a handler in src/gateway/server-methods/system.ts:

export const systemHandlers: GatewayRequestHandlers = {
  "system.echo": ({ params, respond }) => {
    const text = String(params.text ?? "");
    respond(true, { ok: true, text });
  },
};

Register it in src/gateway/server-methods.ts (already merges systemHandlers), then add "system.echo" to METHODS in src/gateway/server.ts.

4. Regenerate

pnpm protocol:check

5. Tests + docs

Add a server test in src/gateway/server.*.test.ts and note the method in docs.

Swift codegen behavior

The Swift generator emits:

• GatewayFrame enum with req, res, event, and unknown cases
• Strongly typed payload structs/enums
• ErrorCode values and GATEWAY_PROTOCOL_VERSION

Unknown frame types are preserved as raw payloads for forward compatibility.

Versioning + compatibility

• PROTOCOL_VERSION lives in src/gateway/protocol/schema.ts.
• Clients send minProtocol + maxProtocol; the server rejects mismatches.
• The Swift models keep unknown frame types to avoid breaking older clients.

Schema patterns and conventions

• Most objects use additionalProperties: false for strict payloads.
• NonEmptyString is the default for IDs and method/event names.
• The top-level GatewayFrame uses a discriminator on type.
• Methods with side effects usually require an idempotencyKey in params (example: send, poll, agent, chat.send).

Live schema JSON

Generated JSON Schema is in the repo at dist/protocol.schema.json. The published raw file is typically available at:

• https://raw.githubusercontent.com/moltbot/moltbot/main/dist/protocol.schema.json 

When you change schemas

1. Update the TypeBox schemas.
2. Run pnpm protocol:check.
3. Commit the regenerated schema + Swift models.