11 tools with basic verb-noun naming and present descriptions, but significant gaps in schema completeness and parameter documentation. All tools return JSON strings rather than structured objects. Most parameter descriptions are minimal (10-30 chars). No output schemas documented. Error handling is absent, tools return raw API responses or generic strings without recovery guidance. Composition is reasonable (single responsibility per tool), but parameter validation and constraint documentation are weak. Naming is clear but descriptions lack LLM-optimization depth (most are 20-60 chars, below the 50-200 char baseline for A+ tools).

• Document output schemas for all tools. E.g., search_invoices returns [{id: int, number: string, client_name: string, status: string, amount: float, due_date: string}]. This enables LLMs to chain tools and extract fields correctly.
• Add enum constraints to parameters. E.g., status in list_expenses should be enum: ['open', 'overdue', 'paid']. Add range constraints: due_days 1-365, limit 1-100. Include these in parameter descriptions, not just JSON Schema.
• Expand tool descriptions to 50-150 chars with WHEN/WHY guidance. E.g., 'List all overdue invoices (past due date). Use this to identify clients who need payment reminders. Returns invoice ID, client name, amount due, and days overdue.'
• Add error recovery guidance. E.g., if FAKTUROID_SENDER_ACCOUNT is missing, return 'Error: FAKTUROID_SENDER_ACCOUNT not set in .env. Set it to format: prefix-number/bank_code (e.g., 123456789/0100). Then retry generate_abo_file.'
• Expose pagination parameters (limit, offset) in search_invoices, list_contacts, list_expenses. Document the default limit (20-30) and max limit in descriptions. Return total_count and next_offset in responses to enable multi-page iteration.