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

With no annotations, the description carries the behavioral burden. It meaningfully discloses that 'Some pricing regimes are approximations rather than an exact tariff', which is an important accuracy limitation for an agent to know. It does not describe output shape or error behavior, but it does surface the key non-obvious trait.

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 purpose and currency, followed by a concise caveat. Every word earns its place and nothing repeats the input 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?

The description explains what the tool computes, the currency, time horizon, and precision caveat. However, without an output schema or annotations, it leaves the exact return value/format and behavior for invalid or unknown places unspecified, keeping it from being fully complete.

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 both from and to are already documented. The description adds the Swiss fare-zone context but does not need to explain parameters further; baseline 3 is appropriate.

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 verb 'Estimates' and object 'monthly cost in CHF of commuting between two Swiss places' make the tool's purpose very clear. It reads as the cost counterpart to the sibling commute_time tool, though it does not explicitly name or differentiate itself from any sibling.

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 implies the use case: estimating monthly transit-pass commuting costs between Swiss locations. It gives no explicit guidance on when to choose commute_cost over commute_time or other sibling tools, and no exclusions or alternative suggestions.

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