DriftLock is a security-focused CI tool for detecting MCP server drift, not a production MCP server itself. The two fixture tools (send_invoice, list_invoices) have clear names and basic schemas, but lack depth in descriptions and parameter documentation. send_invoice has a 127-char description (within baseline 194-char average); list_invoices is only 47 chars. Neither tool documents output schemas, error handling, or recovery guidance. Parameters lack format constraints and validation hints. The 'note' parameter in send_invoice is marked optional but has no default behavior documented. No tool declares permissions, audit requirements, or idempotency guarantees, critical for a tool that sends invoices (a destructive operation).

• Expand list_invoices description to 100 - 150 chars explaining: returns recent invoices with pagination, what fields are included (id, date, amount, recipient), and when to call it (e.g., 'before sending a new invoice, check recent activity').
• Document send_invoice output schema: {confirmation_id: string, timestamp: ISO8601, status: 'sent'|'pending', invoice_url?: string}. This enables agents to reference the confirmation ID in follow-up actions.
• Add error classification to send_invoice: 'Invalid email format' (user-fixable), 'Amount exceeds limit' (user-fixable), 'Service unavailable' (retryable). Include recovery hints: 'Try search_customers() to find the correct email.'
• Declare send_invoice as destructive (idempotentHint: false) and add a dry_run parameter or confirmation step. Agents should not send invoices without explicit intent.
• Add format constraints to parameters: 'to' should validate email format; 'amount' should specify range (e.g., 0.01 - 999999.99 USD); 'limit' in list_invoices should default to 20 and cap at 100.