Spending By Payee

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context beyond annotations: it explains how splits are handled (counted through subtransactions) and that transfers between own accounts are excluded. This is useful edge-case disclosure that helps an agent predict results. It doesn't mention pagination or output format, but with no output schema and read-only semantics, the key behaviors are covered.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences with zero waste. The core function is front-loaded, and the edge-case behaviors (splits, transfers) are packed into the second sentence. Every word earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a read-only aggregation tool with 100% schema coverage and no output schema, the description is nearly complete. It covers the core function, the sort order, the split handling, and the transfer exclusion. The only minor gap is that it doesn't describe the return shape (e.g., whether it returns a list of payee names with amounts), but with no output schema and a clear aggregation description, this is a small gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all parameters (limit, planId, budgetId, sinceDate, untilDate) with defaults and formats. The description adds the conceptual meaning of 'limit' (top N payees by spend) and the date range concept, but doesn't add much beyond the schema. Baseline 3 is appropriate since the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: 'Totals spending per payee over a date range, biggest spend first'. It also adds a helpful real-world framing ('where the money actually goes by merchant') and distinguishes it from related tools by mentioning specific exclusions (splits counted via subtransactions, transfers between own accounts excluded). This is a specific verb+resource with clear scope.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use this tool: when you need spending totals by merchant/payee over a date range. It doesn't explicitly name alternatives or say when not to use it, but the sibling list includes ynab_spending_by_category and ynab_cash_flow, and the description's focus on payees/merchants makes the use case clear. It lacks explicit exclusions or alternative routing, so it doesn't earn a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.