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

Annotations already declare readOnlyHint and openWorldHint, so the description's added value is the commercial/behavioral detail: $0.002 USDC per successful call via x402 (Base, Solana, Arc) and no charge on failure, plus a 'last update' freshness signal. Rate limits and data-refresh cadence are not stated, which keeps it below 5.

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-loaded with the purpose, then the filter capability, then the price. Three sentences with no filler; the field enumeration is long but materially informs the agent about available data, though it borders on restating the output schema.

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?

An output schema exists so return shape needn't be explained, and the description still covers scope, filters, freshness and payment. The main omission is any hint about result volume or how limit interacts with filters, though the schema supplies the limit range.

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 limit, route, state, station and trainNum with examples. The description only restates the filterable dimensions without adding syntax, matching, or precedence rules, so 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 and resource: live Amtrak train status from Amtrak's Track Your Train feed, then enumerates the exact fields returned (train number, route, GPS position, speed, stops). That scope cleanly separates it from the other transit trackers in the sibling list (flightradar24, mbta_realtime, septa_train_view, hk_mtr_realtime) which cover different operators/modes.

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 clear context (live status lookups) and names the available filters, so an agent knows how to narrow a query. It doesn't state when NOT to use it or point to an alternative rail/transit tool, but the Amtrak-only scope makes the intended use obvious.

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