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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds real value beyond that: it discloses the comparison sources (meter tariff, airport flat fare, Uber/Lyft typical prices), the verdict taxonomy (fair/high/overcharged), and the returned next-steps plus refund message.

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?

Front-loaded with the user-facing question and the core action, then the comparison logic and outputs. It is a single dense sentence but every clause earns its place by describing distinct behavior; only the repeated title phrasing is slightly redundant.

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 no output schema, the description carries the return-value burden and does so by naming the verdict values, next steps, and message. It is largely complete for this tool; only the exact output shape and any coverage limits (e.g., which cities are supported) are left unstated.

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 all eight parameters are already documented in the schema, including the 'paid' tip exclusion and the 'when' formats. The description adds no parameter-level syntax or defaults beyond that, so the 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?

States a specific verb and resource — check a fare that was paid — and distinguishes itself from the sibling estimate_fare by anchoring on a completed trip rather than a prospective one. The title's question framing reinforces the intent.

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 phrase 'a fare that was paid' clearly sets the context (post-hoc verification vs. pre-trip estimation), which implicitly routes the agent away from estimate_fare. However, it never names an alternative or states exclusions explicitly, so it falls short of full when/when-not guidance.

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