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

With annotations only telling us it's a non-destructive, open-world mutation, the description carries real weight: it explains the checkout flow, that the tool stops and returns a checkout_url, that card details are never entered, and that it fails for non-rechargeable eSIMs. It also discloses the per-call confirmation default and the API-key/auth requirement, which annotations cannot convey.

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?

Front-loaded with purpose before behavior, and each sentence carries operational value (failure mode, checkout handoff, confirmation policy). The confirmation/Cotlet-policy sentences are somewhat boilerplate, keeping it just short of ideal conciseness.

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 an open-world mutation with no output schema, the description covers what an agent needs: the checkout_url return path, the non-rechargeable failure, confirmation behavior, and auth requirements. Nothing essential 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 description coverage is 100%, so all three parameters are already documented, and the description mostly echoes them ('Set airmoney_usd to apply Airmoney'). It adds minor context (where package_id/esim_id originate) but no syntax or format detail beyond the schema, so 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?

States a specific verb+resource ('Add a top-up package to a rechargeable eSIM') and reinforces scope by noting the package comes from list_topup_packages and the target is an already-installed eSIM. This clearly differentiates it from airalo_buy_esim and airalo_list_topup_packages.

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?

Gives strong context: use it against an eSIM you already installed, package_id comes from list_topup_packages, esim_id from list_esims, and it explicitly fails for non-rechargeable eSIMs. It never names a competing tool (e.g. buy_esim) as the alternative for a fresh purchase, so it stops short of full when-not guidance.

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