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

Annotations only declare readOnlyHint=false and openWorldHint=true; the description goes well beyond that by disclosing the checkout interruption flow, the returned checkout_url, that Cotlet never enters card details, the per-call confirmation default, and the API-key/access requirement. This is exactly the mutation and auth context the annotations do not carry.

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 outcome ('eSIM appears under My eSIMs') is front-loaded and most sentences carry distinct operational facts. It is slightly repetitive, restating the My eSIMs outcome twice, which keeps it from a top score.

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 compensates by describing the return value (checkout_url) and the completion outcome, plus auth, confirmation, and Airmoney constraints. Nothing an agent needs to call this correctly is missing.

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 coverage is already 100%, so the baseline is 3, but the description adds real meaning beyond the schema: it identifies package_id's origin (search_packages) and states that airmoney_usd requires a minimum 1 USD balance, which the schema's 'Default: 0' does not convey.

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 ('Buy a package') and names the upstream source tool (search_packages), making it clearly distinct from siblings like airalo_top_up_esim and airalo_redeem_voucher. An agent can identify the operation without opening the 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?

It gives concrete preconditions (package_id from search_packages, Airmoney balance of at least 1 USD) and the follow-up path (get_install_instructions). However, it never explicitly says when NOT to use this tool versus top_up_esim or redeem_voucher, so routing for an existing eSIM is left to inference.

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