Expose input messages to BeforeInvocationEvent hook#1474
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Unshure merged 5 commits intostrands-agents:mainfrom Jan 15, 2026
Merged
Expose input messages to BeforeInvocationEvent hook#1474Unshure merged 5 commits intostrands-agents:mainfrom
Unshure merged 5 commits intostrands-agents:mainfrom
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Add messages attribute to BeforeInvocationEvent to enable input-side guardrails for PII detection, content moderation, and prompt attack prevention. Hooks can now inspect and modify messages before they are added to the agent's conversation history. - Add writable messages attribute to BeforeInvocationEvent (None default) - Pass messages parameter from _run_loop() to BeforeInvocationEvent - Add unit tests for new messages attribute and writability - Add integration tests for message modification use case - Update docs/HOOKS.md with input guardrails documentation Resolves #8
- Remove detailed Input Guardrails section from docs/HOOKS.md - Simplify BeforeInvocationEvent docstring per review - Remove backward compatibility note from messages attribute - Remove no-op test for messages initialization
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Use concise equality comparison for BeforeInvocationEvent assertions instead of verbose instance checks and property assertions.
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…1474) * feat(hooks): expose input messages to BeforeInvocationEvent Add messages attribute to BeforeInvocationEvent to enable input-side guardrails for PII detection, content moderation, and prompt attack prevention. Hooks can now inspect and modify messages before they are added to the agent's conversation history. - Add writable messages attribute to BeforeInvocationEvent (None default) - Pass messages parameter from _run_loop() to BeforeInvocationEvent - Add unit tests for new messages attribute and writability - Add integration tests for message modification use case - Update docs/HOOKS.md with input guardrails documentation Resolves strands-agents#8 * refactor: address review feedback - Remove detailed Input Guardrails section from docs/HOOKS.md - Simplify BeforeInvocationEvent docstring per review - Remove backward compatibility note from messages attribute - Remove no-op test for messages initialization * refactor: simplify test assertions per review Use concise equality comparison for BeforeInvocationEvent assertions instead of verbose instance checks and property assertions. * Use overwritten messages array for the agent * Fix mypy issue --------- Co-authored-by: Strands Agent <217235299+strands-agent@users.noreply.github.com>
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Description
Add the
messageparameter to theBeforeInvokeHookto provide access to the agent invocation inputs. Today theBeforeInvokeHookonly provides a reference toagent, but this is before the initial message was added to the messages array, so this information is essentially inaccessible at this point. By providing access to messages in this hook, preprocessing can occur before the agent is ever actually invoked (like guardrails or filters).Related Issues
#1006
Documentation PR
N/A
Type of Change
New feature
Testing
How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli
hatch run prepareChecklist
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