Xero MCP server demonstrates above-average definition quality with comprehensive schema coverage, clear naming conventions, and detailed parameter descriptions across 20 tools. All tools follow verb_noun naming patterns (xero_navigate, xero_contacts_list, xero_invoices_create, etc.). Descriptions are consistently present and informative (avg ~150-200 chars), explaining what each tool does and when to use it. Schemas are properly defined with JSON Schema types and constraints (enums for domain/status/type, required fields marked). However, several quality gaps prevent a higher score: (1) output schemas are not documented inline, LLMs cannot see what fields will be returned; (2) tool annotations (readOnlyHint, destructiveHint, idempotentHint) are missing despite clear risk stratification in tool metadata; (3) error handling lacks recovery guidance, tools provide risk classifications (READ_ONLY, WRITE, REVERSIBLE) but tool descriptions do not explain what happens on failure or how to retry; (4) some parameter descriptions could be more prescriptive about formats and constraints (date formats mentioned but not enforced in schema with pattern declarations).

• Document output schemas for all tools. Create a schema map showing field names, types, and descriptions for each response. E.g., xero_contacts_get should declare it returns {contactId: string, Name: string, EmailAddress: string, FirstName: string, LastName: string, Phone: string, Addresses: [...], ...}. This enables LLMs to plan chaining calls (pass returned IDs to subsequent tools).
• Add MCP tool annotations. Wrap WRITE tools (xero_contacts_create, xero_invoices_create, xero_payments_create, xero_invoices_update_status) with destructiveHint: true. Mark all READ_ONLY tools with readOnlyHint: true. Mark idempotent operations (e.g., xero_contacts_get with same ID always returns same result) with idempotentHint: true. This communicates safety properties to clients without requiring documentation.
• Enhance error messages with recovery steps. Update tool descriptions to include 'If this fails, try...'. E.g., xero_contacts_search: 'Search contacts by name. Returns contacts whose name contains the search term. If no matches found, use xero_contacts_list with pagination to browse all contacts.' This guides LLMs through failure modes.
• Enforce date formats in schema. Add 'format': 'date' or 'pattern': '^\d{4}-\d{2}-\d{2}$' to all date parameters (Date, DueDate, fromDate, toDate, date in reports). JSON Schema format validators catch LLM errors before they reach the API.
• Clarify pagination metadata. Update list tool descriptions to state: 'Returns up to 100 items per page. The response includes total count and a next_page_token if more results exist. Use page parameter to fetch subsequent pages.' Then document these response fields in the output schema.