Find eSIM plans for a region

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

Annotations already declare readOnly, idempotent, and non-destructive, but the description adds valuable context beyond that: 'This needs no login,' 'resolves it against the platform's own region list,' and 'The result covers this region only.' It also mentions keeping bundle_code for follow-up, which informs the agent about downstream behavior. This is more than just restating annotations, though it doesn't disclose return formatting (which is covered by the output schema).

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?

The description is about five sentences and each earns its place: it states purpose, gives a WHEN condition, explains region resolution, references the sibling tool for filter/presentation behavior, and notes no login requirement. It is front-loaded with the main action and not overly verbose, though it could be tightened by removing some redundancy like 'such as Europe' and 'The result covers this region only' (both are useful, so not wasted).

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?

Given the tool has an output schema and rich annotations, the description covers the key contextual aspects: when to use it, how to pass the region, that it requires no login, and that it behaves like the country-based sibling. It does not mention edge cases like invalid region codes, but the schema instruction 'Never invent a region code' partially covers that. Overall, it is sufficiently complete for a read-only search tool with a clear usage model.

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 adds a bit of semantic guidance for the region parameter ('Pass the region as the user said it (name or code)') and for filters ('only pass filters the user stated'), but most parameters are already well-documented in the schema. The description does not compensate heavily for parameter semantics, as the schema already does that work.

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+resource: 'Find the multi-country eSIM plans available for one region, such as Europe.' This clearly states what the tool does and distinguishes it from the sibling find_bundles_by_country by emphasizing 'multi-country' and 'region.' It also explicitly says 'The result covers this region only,' reinforcing scope.

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 description includes an explicit 'WHEN' clause: 'the user names a region, or is visiting several countries in the same area.' It also tells the agent to pass the region as the user said it and to filter/present exactly as in find_bundles_by_country, referencing a sibling for consistency. However, it does not explicitly state when not to use this tool (e.g., when a single country is named), so it falls short of a fully explicit exclusion list.

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