Hooks

Hooks let you inject behavior into the agent lifecycle without modifying agents directly. They're the primary extension point in OpenWalrus.

The Hook trait

trait Hook: Send + Sync {
    fn on_build_agent(&self, config: &mut AgentConfig);
    fn on_register_tools(&self, registry: &mut ToolRegistry);
    fn on_event(&self, event: &AgentEvent);
}

Built-in hooks

The daemon composes several hooks into DaemonHook:

Memory as a hook

Every type that implements Memory + Clone + 'static automatically implements Hook. This means any memory backend can be used as a hook — it registers remember and recall tools and injects stored knowledge into the system prompt via on_build_agent.

See memory for details on how knowledge is compiled into prompts.

Composition

DaemonHook dispatches tool calls by name. When an agent invokes a tool, the hook routes it to the correct handler:

• remember / recall → Memory handler
• read / write / bash → OS handler
• search_skill / load_skill → Skill handler
• search_mcp / call_mcp_tool → MCP handler

This keeps tool dispatch centralized and makes it easy to add new tools by adding new sub-hooks.

What's next

• Agents — how agents are configured and executed
• Built-in tools — OsHook details
• Memory — how memory hooks inject knowledge