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

Annotations already cover the read-only/open-world safety profile, and the description still adds real behavioral context: balance is USD-denominated, only applies at checkout when >= 1 USD, cannot cover renewals, and requires a Cotlet API key with app access. Return format/pagination is not described, keeping it short of a 5.

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-loads the resource and unit, and the checkout logic is compact. The first two sentences are mildly redundant, both restating that the balance is returned, which costs a little tightness.

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 zero-param read tool with annotations covering safety, the agent gets currency, business rules, the applies_at_checkout signal, and the auth prerequisite. Only the concrete return shape is left unstated, which is minor given the tool's simplicity.

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?

There are zero input parameters, so the baseline is 4. Nothing further is required or expected from the description here.

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 ('Returns your Airmoney balance') and pins down the unit ('in USD') and domain ('from Airmoney & Membership'). No other sibling in the Airalo set retrieves Airmoney, so the agent can select this unambiguously.

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 explains the checkout rules and the meaning of applies_at_checkout, which is context but not 'when to call this tool vs alternatives'. There is no explicit when-to-use framing or named alternative, so usage is only implied.

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