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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description adds one genuinely useful rule beyond annotations: a shipment counts once per month only when the carrier returned data for it, which explains the counting semantics. It does not cover auth requirements, permissions across companies, or cost/currency behavior.

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, front-loaded with the core purpose and return contents, followed by the one non-obvious counting rule. No filler or redundancy.

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 3-parameter read-only tool with full schema coverage and no output schema, the description covers purpose, default scope, and the counting semantics adequately. Minor gaps remain around multi-company permissions and what cost/currency values represent, but nothing prevents correct invocation.

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 month format, company identifier, and include_shipments. The description adds only the default-month behavior (already in the schema) and no further meaning beyond the shipment-counting rule. 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?

States a specific verb-and-resource: retrieves the company's plan and billable shipment usage for a month, enumerating what is returned (allowance, used, overage, cost, trial end). It is clearly distinct from sibling tools like get_shipment or list_shipments, though it doesn't explicitly name those siblings to route the agent.

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?

Usage is implied by the description (billing/usage questions for a given month, defaulting to this month) but there is no explicit when-to-use vs when-not-to-use guidance or mention of alternatives such as list_shipments for raw shipment listing. The include_shipments flag hints at the boundary with list_shipments, but only indirectly.

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