rmcp-mailer demonstrates solid foundational quality with 29 well-named, verb-prefixed tools organized into logical domains (recipients, groups, templates, email records, events). All tools have descriptions and visible input schemas with typed parameters. However, the server exhibits moderate gaps: (1) descriptions are functional but mostly generic, averaging ~60-80 chars when the baseline suggests 194 chars and optimal 50-200 for LLM reasoning; (2) output schemas are not documented, we cannot verify what fields response objects contain, breaking the chaining principle; (3) error handling is absent from the visible code, no recovery guidance, categorization, or validation error details visible; (4) idempotency and atomic semantics are not declared, creating uncertainty for agent retry logic; (5) some parameter relationships are undocumented (e.g., list_email_records_by_criteria requires 'at least one filter' per description but no mutual exclusion or validation is visible); (6) tool annotations (readOnlyHint, destructiveHint, idempotentHint) are not present in the schema despite the framework supporting them. Risk classification is visible in the assessment but not encoded into the tools themselves. Database-heavy workload is appropriate for the domain, but without response schema documentation and error guidance, downstream LLM reasoning is impaired.

• Document output schemas for all 29 tools. Specify response object structure, field types, and nested objects. Example: 'Returns: {id: integer, name: string, email: string, created_at: ISO8601 datetime, active: boolean}' for new_recipient and find_recipient_by_email.
• Expand tool descriptions from ~65 chars to 100-150 chars. Add context on WHEN to use vs similar tools and what the result enables. Example: 'Find a recipient by email address. Use this when you have an email but not the recipient ID. Returns recipient ID and name for downstream operations like add_recipient_to_group.'
• Add tool annotations to input schemas. Use readOnlyHint: true for list_* and find_* tools, destructiveHint: true for remove_* and send_email, idempotentHint: true for tools that safely retry (new_recipient, new_group, etc.). This enables client-side safety warnings and agent retry policies.
• Implement error response schemas with categorization. Define HTTP 400 (user-fixable: invalid email format, duplicate name), 404 (not found, recoverable with search_*), 409 (conflict, needs user decision), and 500 (retry-able service error). Include recovery hints: 'Email already exists. Try find_recipient_by_email(email) to reuse or update_recipient() to change it.'
• Document parameter relationships explicitly. For list_email_records_by_criteria, clarify: 'Either start_end_time or recipient_id must be provided (or both). Passing neither will fail with code 400.'
• Declare idempotency semantics. For new_* tools, state: 'Idempotent: calling twice with identical input creates one record; agent can safely retry on network errors.' For add_recipient_to_group, state: 'Idempotent: adding the same recipient twice is a no-op; safe to retry.'

Inferred effective spec: <=2025-11-25.

• Relies on Logging (deprecated) - log to stderr or use OpenTelemetry