Strong tool naming and parameter schemas with well-defined enums and constraints. All four tools have clear action-verb names (create_, list_, update_, cancel_) and detailed descriptions. Input schemas are comprehensive using Zod with type definitions and validation rules. However, output schemas are not formally documented, responses are hand-crafted text concatenations rather than structured objects with typed fields. Error handling is basic (returns error text but lacks recovery guidance or categorization). No tool annotations (readOnlyHint, destructiveHint, idempotentHint) despite clear semantic differences between tools (read-only list_reminders vs. destructive cancel_reminder). The server accepts natural identifiers (email, URLs) for recipients, which is good for composition. Missing pagination metadata (total count, next_cursor) in list_reminders response despite accepting limit/offset params.

• Convert text response formatting into structured JSON objects. Define output schema for each tool with explicit fields (id, title, fire_at, channel, recipients, status, delivery_summary). Return objects instead of string concatenations.
• Add tool annotations to server.tool() calls: readOnlyHint=true for list_reminders, destructiveHint=true for cancel_reminder, idempotentHint=true for tools with matching input→output mapping.
• Enhance list_reminders response to include pagination metadata: return {data: [...], count: total, limit, offset, hasMore: bool} so LLM knows when to fetch next page.
• Wrap error handling in a structured error type: {error: true, code: 'INVALID_TIME'|'NOT_FOUND'|'PERMISSION_DENIED', message: '...', retryable: bool, suggestions: ['...']}. Guide LLM on recovery action.
• Add optional dry_run parameter to cancel_reminder, or implement a separate verify_cancellation tool that previews what would be cancelled before committing.
• Document state constraints in tool descriptions: 'update_reminder only works on pending reminders, delivered/failed reminders cannot be modified.' Same for cancel_reminder.
• For create_reminder, specify minimum lead time (e.g. 'fire_at must be at least 1 minute in the future') and add validation with clear error messaging.
• Add per-item error reporting to list_reminders if filtering fails: return {data: [...], errors: [{index, reason}]} instead of complete failure.
• Consider a get_reminder tool to fetch a single reminder by UUID, current API requires listing all and filtering client-side, inefficient for chaining.