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

Annotations already declare readOnlyHint=true and openWorldHint=true, covering safety and open-world assumptions. The description adds value by explicitly stating the reporting philosophy: 'Unknown is reported as unknown, never as bad.' It also hints at the categories of results (which returned nothing, which list exclusions), which gives the agent a preview of the output semantics. This goes beyond the annotations without contradicting them.

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 total with zero filler. The first sentence front-loads the primary action and the breakdown categories, and the second adds a critical nuance ('Unknown is reported as unknown'). Every part earns its place; no redundancy or vague phrasing.

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 lookup with no output schema, the description covers the key output categories (unknown, paid-but-empty, non-serving, monthly spend). It does not describe the exact return format or pagination, but given the moderate complexity and the strong parameter schema, the description is sufficient for an agent to call it correctly. The openWorldHint annotation also sets expectations about unknown items.

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% — the 'dependencies' array and its item properties (url, method, pay_to, calls_per_month) all carry descriptions. The tool description does not add any parameter-level detail beyond what the schema provides, so it rides on the schema. This meets the baseline for full schema coverage.

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 states a specific verb ('look up'), a clear resource ('every paid endpoint your agents call'), and the aggregation dimension ('added up by the address each one pays'). It also lists the specific outcomes (unknown, paid-but-no-response, non-serving, monthly spend). This clearly differentiates it from sibling tools like check_grade or plan_route, which are unrelated to paid endpoint exposure.

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 purpose is so specific that the usage context is obvious: use it when you need a consolidated view of paid endpoints across a fleet. However, there is no explicit statement of when not to use it or mention of alternatives, though siblings are clearly different. The description implies a batch/aggregation scenario without explicitly saying so.

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