Single tool with basic schema and description. Tool name follows verb_noun pattern (send-transactional-email), which is good. Description is 50 chars, within acceptable range but minimal. Input schema is present with proper types (array, string) and descriptions for all three parameters. However, output schema is completely undocumented, the tool returns raw API response text without structure. No error handling guidance, no parameter constraints (e.g., email format validation), and no indication of side effects or idempotency. Error handling catches exceptions but returns unstructured text rather than actionable recovery guidance. Missing: output schema documentation, parameter format constraints, error classification, and confirmation pattern for this destructive operation (sends email).

• Document output schema: return structured object with fields like {success: boolean, messageId: string, timestamp: string, statusCode: number} instead of raw text.
• Add email format validation to toAddresses parameter. Reject invalid addresses with clear error: 'Invalid email address: got "john@invalid", must be valid RFC 5322 format'.
• Implement error classification: return {error: string, category: 'retryable'|'user_fixable'|'fatal', suggestion: string} so LLM knows next action.
• Add idempotency support: accept optional idempotencyKey parameter and document retry behavior. Prevents duplicate sends on agent retry.
• Enhance parameter descriptions: 'subject (1-200 chars, no newlines)', 'content (plaintext, max 10000 chars)', 'toAddresses (array of valid email addresses, 1-100 recipients)'.