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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds value by disclosing the payload contents (plan counts, lowest USD price, ISO codes, page links), which matters because there is no output schema. It doesn't mention rate limits or result size limits, but for a small static catalog that's minor.

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, both earning their place: the first defines scope and return shape, the second handles sibling routing. No filler, and the alternatives come after the definition where they belong.

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 correctly explains what the response contains (destinations, plan counts, lowest price, ISO codes, links). Combined with annotations and the fully described locale enum, an agent has everything needed to invoke and interpret this tool.

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?

The single locale parameter is fully documented in the schema, including allowed values, default, and what it localizes. The description adds no parameter-level detail, so the schema does all the work and baseline 3 applies.

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 (list every country/region with eSIM plans) and enumerates the returned fields, so the agent knows exactly what this call yields. It is clearly distinct from check_coverage and search_plans, which are named.

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?

Explicitly says to use it to find the destination slug for search_plans, and routes the different question (does a plan cover a country) to check_coverage. Both the when and the named alternative are present.

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