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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing that anonymous access is rate limited by MBTA and that each successful call costs $0.002 USDC via x402 (Base, Solana, or Arc) with failed calls not charged. It also notes some fields (occupancy) are only present 'when reported', which is meaningful behavioral nuance for an agent.

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?

Purpose is front-loaded in the first clause, followed by return fields, then cost/rate-limit caveats, all in two sentences with no filler. Every clause carries information an 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 an output schema, full schema coverage, and annotations covering safety, the description supplies exactly the missing pieces: cost model, rate limits, and per-route scoping. Nothing needed to call it correctly is absent.

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 coverage is 100%, so both parameters are already documented. The description adds useful example route ids that the schema lacks, but says nothing about the `limit` parameter or maximum vehicles per call, so it does not materially extend parameter semantics 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?

States a specific verb and resource ('Live MBTA Boston vehicle positions for one route') with concrete example route ids (Red, Orange, Blue, 1), which cleanly separates it from transit siblings such as travel_septa_train_view or travel_hk_mtr_realtime. An agent knows exactly what data comes back 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?

The description makes clear that the tool is scoped to a single route and gives sample route values, which is usable context. However, it never states when to prefer this over other transit tools or what to do for multi-route/whole-system queries, so usage is only implied.

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