Single tool 'send_message' has a clear verb-noun name and adequate description (156 chars), but critical gaps undermine quality. Input schema is present with 6 parameters, all typed and described, meeting baseline requirements. However, output schema is undocumented, the tool returns a dict with 'execution_id', 'response', and optional 'warning' fields, but this structure is never formally declared. Error handling returns dict responses with warning fields rather than actionable recovery guidance. The tool conflates two responsibilities (chat creation + message sending) and lacks idempotency guarantees. No parameter validation, no enum constraints, no pagination support. The description mentions 'use aws___call_aws for investigations' but this external tool is not defined in this server, creating a composition gap.

• Document output schema formally: 'Returns {execution_id: string, response: string, warning?: string}. execution_id persists across turns for multi-turn conversations.'
• Replace generic error messages with actionable guidance. E.g., 'CreateChat failed: invalid agent_space_id. Call list_agent_spaces() to find valid IDs.' or 'SendMessage failed: execution expired. Create a new session with execution_id="".'
• Add idempotency note to description: 'Idempotent: calling with the same execution_id and content returns the same response without duplicate messages.'
• Constrain 'region' parameter with enum of valid AWS regions or add validation: 'AWS region (e.g., us-east-1, eu-west-1). Must be a valid AWS region.'
• Consider splitting into two tools: create_chat_session (returns execution_id) and send_chat_message (requires execution_id). Enables agents to manage session lifecycle explicitly.