The server has basic tool structure with clear naming (send_email, get_unread_emails, create_draft_reply) following verb_noun convention. All three tools have input schemas with JSON Schema format and descriptions present. However, several critical gaps lower the score: (1) parameter descriptions are minimal, 'Recipient email address' and 'Email subject' lack context about format, constraints, or when to use the tool; (2) no documented output schemas, responses are returned as plain text strings, not structured objects; (3) missing error handling guidance, tools throw generic errors like 'Invalid parameters' with no recovery hints; (4) no parameter validation constraints (enums, min/max, patterns) despite tools accepting free-form strings; (5) the 'email_body' parameter in create_draft_reply is marked required but described as optional context, creating ambiguity. Tool descriptions are generic and do not explain selection criteria (e.g., when to use create_draft_reply vs send_email directly). The server implements basic type guards but provides no guidance to the LLM on expected formats or failure modes.

• Document output schemas for all tools. Define send_email to return {success: boolean, message_id: string, timestamp: string}; get_unread_emails to return {total: integer, emails: [{email_id, from, subject, date, summary, full_body}]}; create_draft_reply to return {draft_id: string, url: string, status: string}. This enables LLMs to extract fields for downstream tool calls.
• Add parameter constraints to all tools. For send_email: add 'to' description with 'Valid RFC 5322 email address (e.g., user@example.com)' and regex pattern. For get_unread_emails: constrain 'limit' to 'integer, 1 - 100 (default: 10)' to prevent runaway queries. Use JSON Schema enum, minimum, maximum fields paired with description text.
• Expand tool descriptions to 100 - 150 characters with WHEN and WHY. E.g., send_email: 'Send a composed email immediately via SMTP. Use this after drafting content in conversation. Requires valid recipient email and SMTP credentials configured server-side.' Add a prerequisite note: 'If you need to reply to an existing email, use create_draft_reply instead.'
• Clarify create_draft_reply semantics. Rename 'email_body' to 'original_email_body' (for context only, not required), and add to description: 'Provide the original email body for your reference during reply composition. This tool saves a draft reply you must generate in conversation first.' Update schema to mark email_body as optional if truly not needed for the draft.
• Implement structured error responses. Instead of 'Invalid parameters for send_email', return specific guidance: 'Invalid email address: got "user@example". Expected RFC 5322 format (e.g., user@example.com).' For missing credentials: 'SMTP credentials not configured. Contact administrator to set EMAIL_USER and EMAIL_APP_PASSWORD environment variables.'