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 job is to add context — it does so by disclosing the result cap ('Up to 5 plans'), currency conversion into the user's currency, and the substantive fields returned including coverage type, data-exhaustion behavior, and hotspot/top-up support. It does not state latency, ranking/ordering logic, or what an empty result means.

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 with the purpose and scope front-loaded, followed by a compact inventory of what comes back. The second sentence is a long comma-chained list but every item is informative rather than padding.

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, full parameter coverage, and rich annotations, most burden is already carried by structured fields. The description fills the remaining gap by naming the plan cap and the currency behavior, though it could have said how results are ordered or what happens when no plan matches.

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 the baseline is 3. The description reinforces a few parameters — destination as a place, trip-length framing, and price in the user's currency — but adds nothing about locale, plan_type, or data_gb semantics beyond what the schema already specifies.

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 opens with a specific verb and resource ('Find travel eSIM data plans') and immediately scopes it to one destination plus a trip length, with concrete query examples. That is enough to separate it from siblings like compare_networks or find_destination without opening a schema.

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 scope clause ('for one destination and trip length') implies when the tool applies, and the examples model the expected input shape. However it never names an alternative or an exclusion, so the agent must infer for itself that destination resolution belongs to find_destination and network comparison to compare_networks.

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