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Hooks

Strands' hook system lets you subscribe callbacks to lifecycle events (BeforeToolCallEvent, AfterToolCallEvent, BeforeModelCallEvent, etc.). With the Temporal plugin, hook callbacks run in workflow context — so they must be deterministic — but you can dispatch I/O via activity_as_hook.

This sample wires two callbacks to AfterToolCallEvent:

  1. An in-workflow callback that appends to per-workflow state. Pure data, deterministic across replay.
  2. An activity-backed callback (activity_as_hook(persist_tool_call, ...)) that calls a Temporal activity for the actual audit write. The activity_input= selector pulls a serializable value out of the event.

What This Sample Demonstrates

  • Subscribing multiple callbacks to one hook event
  • Mixing deterministic in-workflow callbacks with off-workflow activity callbacks
  • The activity_input= selector for activity_as_hook

Running the Sample

# Terminal 1
uv run strands_plugin/hooks/run_worker.py

# Terminal 2
uv run strands_plugin/hooks/run_workflow.py

The Temporal UI will show one invoke_model activity per agent turn plus a persist_tool_call activity per tool call.

Files

File Description
workflow.py echo tool, AuditHook (in-workflow + activity-backed), HooksWorkflow
run_worker.py Registers StrandsPlugin + persist_tool_call, starts worker
run_workflow.py Executes the workflow and prints the list of fired events