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

Beyond the read-only annotation, the description discloses pricing, payment mechanism, networks accepted, and that failed calls are not charged. It also names the upstream source and the national-only limitation, giving an agent the operational context needed before invoking a paid read.

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?

The description is front-loaded with the dataset and scope, then immediately states the key limitation, then covers payment. Every sentence carries actionable information with no filler.

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 annotations covering read-only/open-world behavior and an output schema present, the description supplies source, scope, and payment details needed to call the tool. It could be slightly stronger by stating update frequency or units more explicitly, but it is complete for practical selection.

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 schema already documents both parameters with 100% coverage, including defaults and allowed values. The description reiterates the carloads/intermodal distinction and adds FRED series identifiers, but does not materially clarify parameter behavior beyond the schema.

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 dataset and scope: US Class I rail traffic, carloads or intermodal units, from named FRED series with latest values and recent history. It explicitly clarifies that the tool does not provide corridor-by-corridor status, preventing confusion from the tool name.

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?

It clearly says the source is national totals only and cannot answer corridor-level questions, which is valuable usage guidance. It does not name a specific sibling alternative for corridor-level data, so it falls short of explicit routing guidance.

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