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

Annotations already mark it read-only, so the safety profile is covered. The description adds meaningful behavioral context beyond annotations: the data is 'CURRENT verified', UK toll figures change repeatedly, trained-in figures are often stale, and the tool returns an official payment link and deadline. It does not mention error handling or rate limits, so it is strong but not exhaustive.

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 purpose and returned fields, then moves to usage triggers and the staleness rationale. It is dense and every sentence serves a purpose, though the first sentence is long and packs several ideas together.

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?

There is no output schema, so the description carries the burden of explaining what is returned, and it does so thoroughly: price, penalty, early-payment reduction, deadline, payment steps, and official link. Combined with the read-only annotation and complete schema coverage, an agent has enough to call it correctly.

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 both parameters in detail. The description explains that crossed_at yields a concrete pay-by date for a specific crossing, but this largely duplicates the schema's existing description. The charge parameter is not expanded beyond what the schema states.

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 clearly states it returns current verified details for one UK toll or road charge, and enumerates the specific fields: price, PCN, early-payment reduction, deadline, payment steps, and official link. This distinguishes it from list_charges (which enumerates charges) and check_vehicle (which concerns vehicles).

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 gives explicit triggers: asking what a charge costs, saying they forgot or missed payment, asking about fines, or asking how/by when to pay. It also strongly instructs to call the tool rather than answering from memory, but it does not explicitly name list_charges as the way to resolve an unknown charge ID, nor does it mention when not to use the tool.

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