Hooks

Hooks let you intercept and modify OpenClaw’s behavior at key lifecycle points. Hooks are registered via the Plugin API and called synchronously or asynchronously depending on the event type.

Registering Hooks

Use api.registerHook to register a hook handler:

import type { OpenClawPluginApi } from "openclaw/plugin-sdk";

const plugin = {
  id: "my-plugin",
  register(api: OpenClawPluginApi) {
    api.registerHook("llm_input", async (event, ctx) => {
      api.logger.info(`LLM call: ${event.provider}/${event.model}`);
    });
  }
};

export default plugin;

You can register multiple events at once:

api.registerHook(["message_received", "message_sent"], async (event, ctx) => {
  api.logger.info(`Message event: ${JSON.stringify(event)}`);
});

Available Hooks

Agent Lifecycle

before_model_resolve

Fired before resolving the model/provider for an agent run. Use this to override model selection based on the prompt.

api.registerHook("before_model_resolve", async (event, ctx) => {
  // event.prompt: string
  // ctx: { agentId?, sessionKey?, workspaceDir?, messageProvider? }
  
  if (event.prompt.includes("image")) {
    return {
      modelOverride: "gpt-4-vision-preview",
      providerOverride: "openai"
    };
  }
});

Event: { prompt: string } Return: { modelOverride?: string, providerOverride?: string } or void

before_prompt_build

Fired before building the prompt for an agent run. Session messages are available at this point.

api.registerHook("before_prompt_build", async (event, ctx) => {
  // event.prompt: string
  // event.messages: unknown[]
  // ctx: { agentId?, sessionKey?, workspaceDir?, messageProvider? }
  
  return {
    systemPrompt: "Custom system prompt",
    prependContext: "Additional context"
  };
});

Event: { prompt: string, messages: unknown[] } Return: { systemPrompt?: string, prependContext?: string } or void

before_agent_start (legacy)

Fired before an agent run starts. Combines both before_model_resolve and before_prompt_build phases.

api.registerHook("before_agent_start", async (event, ctx) => {
  return {
    modelOverride: "gpt-4",
    systemPrompt: "Custom prompt"
  };
});

Event: { prompt: string, messages?: unknown[] } Return: { modelOverride?: string, providerOverride?: string, systemPrompt?: string, prependContext?: string } or void

llm_input

Fired before sending a prompt to the LLM. Use for logging, telemetry, or analytics.

api.registerHook("llm_input", async (event, ctx) => {
  api.logger.info(
    `LLM call: ${event.provider}/${event.model}, ` +
    `prompt length: ${event.prompt.length}, ` +
    `history: ${event.historyMessages.length} messages`
  );
});

Event:

{
  runId: string;
  sessionId: string;
  provider: string;
  model: string;
  systemPrompt?: string;
  prompt: string;
  historyMessages: unknown[];
  imagesCount: number;
}

llm_output

Fired after receiving a response from the LLM.

api.registerHook("llm_output", async (event, ctx) => {
  api.logger.info(
    `LLM response: ${event.assistantTexts.length} messages, ` +
    `tokens: ${event.usage?.total ?? 0}`
  );
});

Event:

{
  runId: string;
  sessionId: string;
  provider: string;
  model: string;
  assistantTexts: string[];
  lastAssistant?: unknown;
  usage?: {
    input?: number;
    output?: number;
    cacheRead?: number;
    cacheWrite?: number;
    total?: number;
  };
}

agent_end

Fired after an agent run completes (success or failure).

api.registerHook("agent_end", async (event, ctx) => {
  api.logger.info(
    `Agent run ${event.success ? "succeeded" : "failed"}, ` +
    `duration: ${event.durationMs}ms`
  );
});

Event:

{
  messages: unknown[];
  success: boolean;
  error?: string;
  durationMs?: number;
}

Session Management

session_start

Fired when a new session starts.

api.registerHook("session_start", async (event, ctx) => {
  api.logger.info(`Session started: ${event.sessionId}`);
});

Event: { sessionId: string, resumedFrom?: string }

session_end

Fired when a session ends.

api.registerHook("session_end", async (event, ctx) => {
  api.logger.info(
    `Session ended: ${event.sessionId}, ` +
    `${event.messageCount} messages, ` +
    `duration: ${event.durationMs}ms`
  );
});

Event: { sessionId: string, messageCount: number, durationMs?: number }

before_compaction

Fired before session compaction (history summarization). Useful for archiving session history.

api.registerHook("before_compaction", async (event, ctx) => {
  api.logger.info(
    `Compacting ${event.compactingCount} messages, ` +
    `total: ${event.messageCount}`
  );
  
  // Read full session history from disk if needed
  if (event.sessionFile) {
    const fs = await import("node:fs/promises");
    const lines = await fs.readFile(event.sessionFile, "utf-8");
    // Process lines...
  }
});

Event:

{
  messageCount: number;
  compactingCount?: number;
  tokenCount?: number;
  messages?: unknown[];
  sessionFile?: string;
}

after_compaction

Fired after session compaction completes.

api.registerHook("after_compaction", async (event, ctx) => {
  api.logger.info(
    `Compaction complete: ${event.compactedCount} messages kept`
  );
});

Event: { messageCount: number, tokenCount?: number, compactedCount: number, sessionFile?: string }

before_reset

Fired when a session is reset (/new, /reset commands).

api.registerHook("before_reset", async (event, ctx) => {
  api.logger.info(`Session reset: ${event.reason ?? "unknown"}`);
});

Event: { sessionFile?: string, messages?: unknown[], reason?: string }

Message Flow

message_received

Fired when a message is received from a channel.

api.registerHook("message_received", async (event, ctx) => {
  api.logger.info(
    `Message from ${event.from}: ${event.content.slice(0, 50)}`
  );
});

Event: { from: string, content: string, timestamp?: number, metadata?: Record<string, unknown> } Context: { channelId: string, accountId?: string, conversationId?: string }

message_sending

Fired before sending a message to a channel. Can modify or cancel the message.

api.registerHook("message_sending", async (event, ctx) => {
  // Filter profanity
  const filtered = event.content.replace(/badword/gi, "***");
  return { content: filtered };
});

Event: { to: string, content: string, metadata?: Record<string, unknown> } Return: { content?: string, cancel?: boolean } or void Context: { channelId: string, accountId?: string, conversationId?: string }

message_sent

Fired after a message is sent to a channel.

api.registerHook("message_sent", async (event, ctx) => {
  if (event.success) {
    api.logger.info(`Message sent to ${event.to}`);
  } else {
    api.logger.error(`Failed to send: ${event.error}`);
  }
});

Event: { to: string, content: string, success: boolean, error?: string } Context: { channelId: string, accountId?: string, conversationId?: string }

Tool Execution

before_tool_call

Fired before a tool is called. Can modify parameters or block the call.

api.registerHook("before_tool_call", async (event, ctx) => {
  if (event.toolName === "delete_file" && !event.params.confirmed) {
    return {
      block: true,
      blockReason: "Destructive operation requires confirmation"
    };
  }
});

Event: { toolName: string, params: Record<string, unknown> } Return: { params?: Record<string, unknown>, block?: boolean, blockReason?: string } or void Context: { agentId?: string, sessionKey?: string, toolName: string }

after_tool_call

Fired after a tool completes.

api.registerHook("after_tool_call", async (event, ctx) => {
  api.logger.info(
    `Tool ${event.toolName} ${event.error ? "failed" : "succeeded"}, ` +
    `duration: ${event.durationMs}ms`
  );
});

Event: { toolName: string, params: Record<string, unknown>, result?: unknown, error?: string, durationMs?: number } Context: { agentId?: string, sessionKey?: string, toolName: string }

tool_result_persist

Fired before writing a tool result to the session transcript. Can modify or drop the message.

api.registerHook("tool_result_persist", (event, ctx) => {
  // Strip large responses to save space
  if (event.message.content?.length > 10000) {
    return {
      message: {
        ...event.message,
        content: event.message.content.slice(0, 1000) + "... (truncated)"
      }
    };
  }
});

Event: { toolName?: string, toolCallId?: string, message: AgentMessage, isSynthetic?: boolean } Return: { message?: AgentMessage } or void

before_message_write

Fired before writing any message to the session transcript. Can block the write.

api.registerHook("before_message_write", (event, ctx) => {
  // Don't persist system messages
  if (event.message.role === "system") {
    return { block: true };
  }
});

Event: { message: AgentMessage, sessionKey?: string, agentId?: string } Return: { block?: boolean, message?: AgentMessage } or void

Gateway Lifecycle

gateway_start

Fired when the gateway starts.

api.registerHook("gateway_start", async (event, ctx) => {
  api.logger.info(`Gateway started on port ${event.port}`);
});

Event: { port: number } Context: { port?: number }

gateway_stop

Fired when the gateway stops.

api.registerHook("gateway_stop", async (event, ctx) => {
  api.logger.info(`Gateway stopped: ${event.reason ?? "unknown"}`);
});

Event: { reason?: string } Context: { port?: number }

Hook Files (Advanced)

OpenClaw also supports hook files with frontmatter metadata. These are typically used for bundled hooks in src/hooks/bundled/. Hook directory structure:

hooks/
  my-hook/
    HOOK.md
    handler.ts

HOOK.md:

---
events:
  - llm_input
  - llm_output
---

# My Hook

Description of what this hook does.

handler.ts:

import type { InternalHookEvent, InternalHookContext } from "openclaw/plugin-sdk";

export default async function handler(event: InternalHookEvent, ctx: InternalHookContext) {
  // Handle event
}

Plugins can register hook directories:

import { registerPluginHooksFromDir } from "openclaw/plugin-sdk";

register(api: OpenClawPluginApi) {
  await registerPluginHooksFromDir(api, "./hooks");
}

See src/hooks/plugin-hooks.ts for details.

Example: Session Logger

import type { OpenClawPluginApi } from "openclaw/plugin-sdk";
import { writeFile } from "node:fs/promises";

const plugin = {
  id: "session-logger",
  register(api: OpenClawPluginApi) {
    const sessionLog = new Map<string, any>();

    api.registerHook("session_start", async (event) => {
      sessionLog.set(event.sessionId, {
        startTime: Date.now(),
        llmCalls: 0,
        toolCalls: 0
      });
    });

    api.registerHook("llm_input", async (event) => {
      const log = sessionLog.get(event.sessionId);
      if (log) log.llmCalls++;
    });

    api.registerHook("after_tool_call", async (event, ctx) => {
      const sessionId = ctx.sessionKey;
      const log = sessionId && sessionLog.get(sessionId);
      if (log) log.toolCalls++;
    });

    api.registerHook("session_end", async (event) => {
      const log = sessionLog.get(event.sessionId);
      if (log) {
        const report = {
          sessionId: event.sessionId,
          duration: Date.now() - log.startTime,
          messageCount: event.messageCount,
          llmCalls: log.llmCalls,
          toolCalls: log.toolCalls
        };
        await writeFile(
          `/tmp/session-${event.sessionId}.json`,
          JSON.stringify(report, null, 2)
        );
        sessionLog.delete(event.sessionId);
      }
    });
  }
};

export default plugin;

Next Steps

Tools - Build custom agent tools
Channels - Create channel integrations
Examples - Real-world plugin examples

Overview

SDK Reference

Extensions

Registering Hooks

Available Hooks

Agent Lifecycle

before_model_resolve

before_prompt_build

before_agent_start (legacy)

llm_input

llm_output

agent_end

Session Management

session_start

session_end

before_compaction

after_compaction

before_reset

Message Flow

message_received

message_sending

message_sent

Tool Execution

before_tool_call

after_tool_call

tool_result_persist

before_message_write

Gateway Lifecycle

gateway_start

gateway_stop

Hook Files (Advanced)

Example: Session Logger

Next Steps

Overview

SDK Reference

Extensions

​Registering Hooks

​Available Hooks

​Agent Lifecycle

​before_model_resolve

​before_prompt_build

​before_agent_start (legacy)

​llm_input

​llm_output

​agent_end

​Session Management

​session_start

​session_end

​before_compaction

​after_compaction

​before_reset

​Message Flow

​message_received

​message_sending

​message_sent

​Tool Execution

​before_tool_call

​after_tool_call

​tool_result_persist

​before_message_write

​Gateway Lifecycle

​gateway_start

​gateway_stop

​Hook Files (Advanced)

​Example: Session Logger

​Next Steps

Registering Hooks

Available Hooks

Agent Lifecycle

before_model_resolve

before_prompt_build

before_agent_start (legacy)

llm_input

llm_output

agent_end

Session Management

session_start

session_end

before_compaction

after_compaction

before_reset

Message Flow

message_received

message_sending

message_sent

Tool Execution

before_tool_call

after_tool_call

tool_result_persist

before_message_write

Gateway Lifecycle

gateway_start

gateway_stop

Hook Files (Advanced)

Example: Session Logger

Next Steps