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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered by structured data. The description goes beyond that by disclosing what a row contains (each operator, its best generation, how many plans use it, the cheapest one), which is the kind of added context that matters. It does not discuss ordering, coverage gaps, or fallback behavior for destinations with no operators.

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, no filler: the purpose and the question patterns come first, the multi-country parameter caveat second. Every clause earns its place and nothing is repeated across sentences.

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 four parameters, one required, full schema coverage, an output schema present, and comprehensive annotations, the remaining burden on the description is purpose and routing, both delivered. An agent has everything needed to decide to call it and which parameters to set.

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 destination, country, currency and locale are already documented in the schema, and the description only restates the country behavior for multi-country destinations. Nothing is added about locale/currency effects beyond what the enum and pattern already specify. 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?

"Compare the local mobile networks for a destination side by side" gives a specific verb (compare) and resource (mobile networks per destination), and the description enumerates the exact output facets (operator, best generation, plan count, cheapest plan). This clearly separates it from search_plans, which returns plans rather than a network comparison.

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?

Concrete trigger questions ('which network is best in Thailand', 'which eSIM has 5G in Tokyo') make the intended use unambiguous, and the multi-country conditional ('pass country to see that country's operators') tells the agent when to use an optional parameter. It stops short of naming alternatives (search_plans, plan_trip) or stating when not to use it.

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