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

Annotations only cover safety (readOnly, non-destructive, open-world), yet the description adds the real behavioral payload: the USDOT rail-access check, the 50-mile threshold, the available:false + reason fallback instead of a price, and the per-call quota against the monthly FreightFA allowance. None of this is derivable from the annotations or schema.

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?

Four sentences, front-loaded with the purpose and then layering the access-check behavior, the caveat, and the billing note. Each sentence carries information; only the 'directional benchmark' sentence is somewhat soft.

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 does real work explaining the failure return shape (available:false plus reason) and the nature of the result. It stops short of describing the successful price payload's structure, which an agent calling without an output schema might want.

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 baseline is 3. The description restates that origin/destination enable the rail access check, which the schema already documents ('Recommended: enables the rail access check'), so it adds little semantics beyond the structured fields.

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 with scope: 'Estimate a Class I carload rail freight rate for a commodity, distance, and weight.' That immediately separates it from the sibling estimators (estimate_barge_rate, estimate_intermodal_rate, estimate_ltl_rate, estimate_truckload_rate, estimate_network_cost).

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?

Gives a clear triggering condition for the origin/destination inputs and an explicit exclusion: 'Don't quote rail on such a lane.' It also frames the output as a planning benchmark rather than a firm quote. It doesn't route the agent to an alternative tool when rail is unavailable, which keeps it short of a 5.

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