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

Annotations provide readOnlyHint true, and the description does not contradict. It adds behavioral context: 'CURRENT verified details' implies dynamic data, and notes that toll prices change frequently, which is a key behavioral trait. However, other behaviors like rate limits or error conditions are not mentioned.

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 a single dense paragraph that front-loads key outputs and usage. Every sentence adds value, but it could be slightly more structured (e.g., bullet points) for easier scanning. Still, it's concise and efficient.

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?

Given no output schema, the description lists what is returned (price, penalty, etc.) and how to get specific pay-by dates. It covers return values and usage context. However, it does not mention error handling or invalid charge inputs, leaving a minor gap for a query tool.

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% with descriptions. The description adds value by explaining that passing cross_at yields a concrete pay-by date, and that charge accepts IDs from list_charges or common names—enhancing understanding 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 clearly identifies the tool's purpose: providing verified details for UK toll/road charges, including price, penalty, deadline, and payment instructions. It distinguishes from siblings like list_charges (lists IDs) and check_vehicle (vehicle-specific checks) through specific output details.

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 explicitly states when to use the tool: 'whenever someone asks what a charge costs, says they forgot or missed a payment, asks about the fine/penalty, or asks how or by when to pay'. It also advises to always call this tool rather than relying on memory, providing clear context and alternatives.

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