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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's real contribution is the selection algorithm: cheapest plan that covers each stop's days at the daily data need. That is genuine behavioral context an agent would not get from the annotations. It omits the 8-stop cap and any statement about how ties or uncovered routes are handled.

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?

A single dense sentence that front-loads the multi-country scenario and immediately follows with a concrete example. Every clause carries information, though the nested comparison logic reads as slightly run-on.

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 an output schema present and rich annotations, the description only needs to explain inputs and selection logic, which it largely does. Remaining gaps are minor: the maxItems=8 trip limit and what happens when no regional plan covers all stops are not mentioned.

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%, so the schema documents locale, currency, and data_gb_per_day itself. The description nevertheless adds meaning to the stops array by illustrating the country/days pairing and tying 'daily data need' to the per-day data parameter, which goes beyond the schema text.

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 states the job concretely: compare one regional plan covering every stop against a separate plan per country, choosing the cheapest option for each stop's days at the given daily data need. The example (Japan 7 days, then Korea 5 days) makes the resource unambiguous. It does not differentiate from the sibling search_plans, so it stops short of a 5.

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 multi-country scenario and worked example imply when the tool applies, but there is no explicit guidance such as 'use this instead of search_plans for single-country trips' or any stated exclusions. The agent must infer the boundary from the sibling name alone.

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