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

Annotations already establish read-only behavior, and the description adds meaningful context beyond that: cheapest-first ordering, included plan attributes, data-only/no-phone-number limitation, and unlocked-device requirement. It does not describe pagination or other operational limits, but the added behavioral detail is solid.

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 definition is compact and front-loads the core purpose before adding eligibility details. Every sentence is useful, though the first sentence is dense and could be slightly easier to scan.

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?

For a simple read-only lookup tool with annotations, full schema coverage, and an output schema, the description gives an agent enough to call it correctly: destination scope, filters, ordering, returned fields, and device/data constraints. It could be slightly stronger by explicitly contrasting with the purchase sibling.

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 schema already carries the parameter semantics. The description adds marginal value by mentioning 'global' as a destination and framing min_days as trip length, but does not materially deepen parameter understanding beyond the schema.

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 uses a specific verb ('Lists') and resource ('Inbox eSIM data plans') and clearly scopes it to a travel destination while stating ordering and returned fields. It is readily distinguishable from the purchase-oriented sibling 'buy_esim'.

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?

It gives useful context for use (travel destination, data-only plans, unlocked eSIM phones), but it does not explicitly say when to use this versus 'buy_esim' or name any exclusions. The usage is implied rather than directly guided.

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