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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral context: this is a monthly snapshot, the haul basis is fixed at 750 miles, and the payload includes 1-, 3- and 12-month deltas plus 52-week high/low — enough to tell an agent what the numbers mean before calling.

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?

A single sentence with zero filler, front-loading the scope (this month's, US national) before the qualifying details. Every clause — truck type, haul length, change windows, 52-week range — carries information the agent needs.

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 parameters and no output schema, the description carries the full burden and does well: it enumerates the metrics returned. Minor gaps remain — it does not say which truck types exist (a sibling apparently lists equipment) or whether the change figures are percentages or dollar amounts.

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?

The tool takes no parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description correctly spends its words on defining the fixed measurement basis (750-mile haul, national average) instead of inventing parameter guidance.

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 names a specific resource (US national average truckload rate per mile) and pins down the exact scope: every truck type, a 750-mile haul, current month. The word 'national' plus 'this month's' implicitly separates it from siblings like get_state_rates and get_rate_history, so an agent can select it without opening the 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?

Usage is only implied: 'this month's' signals a current-snapshot tool rather than a historical or lane-specific one, which nudges an agent away from get_lane_rate_history or estimate_lane_rate. However, no alternative is named and there is no explicit when-to-use or when-not-to-use statement.

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