Observability

Agents emit structured events for every significant operation — RPC calls, state changes, schedule execution, workflow transitions, MCP connections, and more. These events are published to diagnostics channels and are silent by default (zero overhead when nobody is listening).

Event structure

Every event has these fields:

{
  type: "rpc",                        // what happened
  agent: "MyAgent",                   // which agent class emitted it
  name: "user-123",                   // which agent instance (Durable Object name)
  payload: { method: "getWeather" },  // details
  timestamp: 1758005142787            // when (ms since epoch)
}

agent and name identify the source agent — agent is the class name and name is the Durable Object instance name.

Channels

Events are routed to eight named channels based on their type:

Channel	Event types	Description
`agents:state`	`state:update`	State sync events
`agents:rpc`	`rpc`, `rpc:error`	RPC method calls and failures
`agents:message`	`message:request`, `message:response`, `message:clear`, `message:cancel`, `message:error`, `tool:result`, `tool:approval`	Chat message and tool lifecycle
`agents:schedule`	`schedule:create`, `schedule:execute`, `schedule:cancel`, `schedule:retry`, `schedule:error`, `queue:create`, `queue:retry`, `queue:error`	Scheduled and queued task lifecycle
`agents:lifecycle`	`connect`, `disconnect`, `destroy`	Agent connection and teardown
`agents:workflow`	`workflow:start`, `workflow:event`, `workflow:approved`, `workflow:rejected`, `workflow:terminated`, `workflow:paused`, `workflow:resumed`, `workflow:restarted`	Workflow state transitions
`agents:mcp`	`mcp:client:preconnect`, `mcp:client:connect`, `mcp:client:authorize`, `mcp:client:discover`	MCP client operations
`agents:email`	`email:receive`, `email:reply`	Email processing

Subscribing to events

The subscribe() function from agents/observability provides type-safe access to events on a specific channel:

JavaScript
TypeScript

import { subscribe } from "agents/observability";

const unsub = subscribe("rpc", (event) => {
  if (event.type === "rpc") {
    console.log(`RPC call: ${event.payload.method}`);
  }
  if (event.type === "rpc:error") {
    console.error(
      `RPC failed: ${event.payload.method} — ${event.payload.error}`,
    );
  }
});

// Clean up when done
unsub();

import { subscribe } from "agents/observability";

const unsub = subscribe("rpc", (event) => {
  if (event.type === "rpc") {
    console.log(`RPC call: ${event.payload.method}`);
  }
  if (event.type === "rpc:error") {
    console.error(
      `RPC failed: ${event.payload.method} — ${event.payload.error}`,
    );
  }
});

// Clean up when done
unsub();

The callback is fully typed — event is narrowed to only the event types that flow through that channel.

Raw diagnostics_channel

You can also subscribe directly using the Node.js API:

JavaScript
TypeScript

import { subscribe } from "node:diagnostics_channel";

subscribe("agents:schedule", (event) => {
  console.log(event);
});

import { subscribe } from "node:diagnostics_channel";

subscribe("agents:schedule", (event) => {
  console.log(event);
});

Tail Workers (production)

In production, all diagnostics channel messages are automatically forwarded to Tail Workers. No subscription code is needed in the agent itself — attach a Tail Worker and access events via event.diagnosticsChannelEvents:

JavaScript
TypeScript

export default {
  async tail(events) {
    for (const event of events) {
      for (const msg of event.diagnosticsChannelEvents) {
        // msg.channel is "agents:rpc", "agents:workflow", etc.
        // msg.message is the typed event payload
        console.log(msg.timestamp, msg.channel, msg.message);
      }
    }
  },
};

export default {
  async tail(events) {
    for (const event of events) {
      for (const msg of event.diagnosticsChannelEvents) {
        // msg.channel is "agents:rpc", "agents:workflow", etc.
        // msg.message is the typed event payload
        console.log(msg.timestamp, msg.channel, msg.message);
      }
    }
  },
};

This gives you structured, filterable observability in production with zero overhead in the agent hot path.

Custom observability

You can override the default implementation by providing your own Observability interface:

JavaScript
TypeScript

import { Agent } from "agents";
const myObservability = {
  emit(event) {
    // Send to your logging service, filter events, etc.
    if (event.type === "rpc:error") {
      console.error(event.payload.method, event.payload.error);
    }
  },
};

class MyAgent extends Agent {
  observability = myObservability;
}

import { Agent } from "agents";
import type { Observability } from "agents/observability";

const myObservability: Observability = {
  emit(event) {
    // Send to your logging service, filter events, etc.
    if (event.type === "rpc:error") {
      console.error(event.payload.method, event.payload.error);
    }
  },
};

class MyAgent extends Agent {
  override observability = myObservability;
}

Set observability to undefined to disable all event emission:

JavaScript
TypeScript

import { Agent } from "agents";

class MyAgent extends Agent {
  observability = undefined;
}

import { Agent } from "agents";

class MyAgent extends Agent {
  override observability = undefined;
}

Event reference

RPC events

Type	Payload	When
`rpc`	`{ method, streaming? }`	A `@callable` method is invoked
`rpc:error`	`{ method, error }`	A `@callable` method throws

State events

Type	Payload	When
`state:update`	`{}`	`setState()` is called

Message and tool events (AIChatAgent)

These events are emitted by AIChatAgent from @cloudflare/ai-chat. They track the chat message lifecycle, including client-side tool interactions.

Type	Payload	When
`message:request`	`{}`	A chat message is received
`message:response`	`{}`	A chat response stream completes
`message:clear`	`{}`	Chat history is cleared
`message:cancel`	`{ requestId }`	A streaming request is cancelled
`message:error`	`{ error }`	A chat stream fails
`tool:result`	`{ toolCallId, toolName }`	A client tool result is received
`tool:approval`	`{ toolCallId, approved }`	A tool call is approved or rejected

Schedule and queue events

Type	Payload	When
`schedule:create`	`{ callback, id }`	A schedule is created
`schedule:execute`	`{ callback, id }`	A scheduled callback starts
`schedule:cancel`	`{ callback, id }`	A schedule is cancelled
`schedule:retry`	`{ callback, id, attempt, maxAttempts }`	A scheduled callback is retried
`schedule:error`	`{ callback, id, error, attempts }`	A scheduled callback fails after all retries
`queue:create`	`{ callback, id }`	A task is enqueued
`queue:retry`	`{ callback, id, attempt, maxAttempts }`	A queued callback is retried
`queue:error`	`{ callback, id, error, attempts }`	A queued callback fails after all retries

Lifecycle events

Type	Payload	When
`connect`	`{ connectionId }`	A WebSocket connection is established
`disconnect`	`{ connectionId, code, reason }`	A WebSocket connection is closed
`destroy`	`{}`	The agent is destroyed

Workflow events

Type	Payload	When
`workflow:start`	`{ workflowId, workflowName? }`	A workflow instance is started
`workflow:event`	`{ workflowId, eventType? }`	An event is sent to a workflow
`workflow:approved`	`{ workflowId, reason? }`	A workflow is approved
`workflow:rejected`	`{ workflowId, reason? }`	A workflow is rejected
`workflow:terminated`	`{ workflowId, workflowName? }`	A workflow is terminated
`workflow:paused`	`{ workflowId, workflowName? }`	A workflow is paused
`workflow:resumed`	`{ workflowId, workflowName? }`	A workflow is resumed
`workflow:restarted`	`{ workflowId, workflowName? }`	A workflow is restarted

MCP events

Type	Payload	When
`mcp:client:preconnect`	`{ serverId }`	Before connecting to an MCP server
`mcp:client:connect`	`{ url, transport, state, error? }`	An MCP connection attempt completes or fails
`mcp:client:authorize`	`{ serverId, authUrl, clientId? }`	An MCP OAuth flow begins
`mcp:client:discover`	`{ url?, state?, error?, capability? }`	MCP capability discovery succeeds or fails

Email events

Type	Payload	When
`email:receive`	`{ from, to, subject? }`	An email is received
`email:reply`	`{ from, to, subject? }`	A reply email is sent

Next steps

Configuration wrangler.jsonc setup and deployment.

Tail Workers Forward diagnostics channel events to a Tail Worker for production monitoring.

Agents API Complete API reference for the Agents SDK.