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

No annotations, so the description carries the full burden and does: it discloses that reads are free ('Reading costs nothing'), that an API key must be supplied on the Authorization header, that counts are uncapped unlike list_payments, and what chargedNotDelivered means and implies. This is unusually rich behavioral disclosure for a read tool.

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?

Front-loads what is counted, then the return shape, then the semantic caveat, then routing and auth. Every clause earns its place; nothing is redundant padding.

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?

With no output schema, the description compensates by explaining the three returned fields (total, series with date/value, chargedNotDelivered) plus auth and cost. Nothing needed to call or interpret it correctly is missing.

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 coverage is 100% and both parameters (to/from, ISO-8601 inclusive bounds) are fully documented there. The description refers to 'the period' but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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?

States a specific verb+resource ('Count your Router payment requests') and immediately scopes it against siblings: 'not money... use get_budget... for amounts per payment use list_payments.' An agent can identify this tool versus list_payments and get_budget without opening any schema.

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?

Explicit routing: use get_budget for spend/remaining, list_payments for per-payment amounts, and this tool for counts. It also gives a downstream action rule ('flag a non-zero count to the user'), which is usage guidance beyond mere selection.

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