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

With no annotations, the description carries the full burden and does disclose real behavioral traits: the pricing formula, penalty inclusion, and the chargeable=false fallback that returns a list of zones where the vehicle class would be charged. It omits error/permission behavior, but the response semantics are unusually well covered.

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?

Two sentences, front-loaded with the core computation, with the non-charged fallback second. No filler, nothing that could be cut without losing information.

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?

No output schema exists, so the description's explanation of the return shape (cost, chargeable flag, alternative zone list) is doing necessary work. It is nearly complete for a 4-param tool, with the only omission being guidance on when to prefer it over sibling tools.

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 75%, but the description still adds value by tying 'days' and 'unpaid' to the cost formula and clarifying that the non-charged branch returns alternative zones. The zone parameter remains unexplained in both places, which is the only real gap.

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 ('Cost one trip through a zone') and even gives the computation formula (daily rate x days + penalty). It is clearly distinguishable from list_zones and zone_charges in intent, though it never names those siblings to make the boundary explicit.

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?

There is no explicit when-to-use guidance and no comparison to list_zones or zone_charges, which an agent could plausibly reach for first to obtain rates. Usage is only inferable from the phrase 'Cost one trip through a zone'.

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