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

Annotations already establish read-only, idempotent, open-world behavior, so the safety profile is covered. The description adds genuinely new behavioral context: the data is live and currently purchasable, the drill-down must be done stepwise, and only fixed-price plans are payable downstream. It does not discuss pagination or result-size limits, minor for a read-only listing tool.

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?

Five short sentences, front-loaded with the resource, then the drill-down progression, then the critical routing and hard constraint. Every sentence carries a distinct instruction and none is redundant.

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?

No output schema exists, and the description compensates by naming what each level returns (countries, product types, operators, plans with exact codes, foreign-currency price, NGN-equivalent cost). Combined with the payment constraints, an agent has everything needed to call this correctly.

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 100%, so the baseline is 3. The description adds value by explaining the sequential dependency between the parameters — each value is an output of the previous level and must be passed back verbatim rather than invented — which the per-field schema text does not convey as a whole.

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 — browsing the live international top-up catalogue — and immediately clarifies scope (170+ countries, hierarchical drill-down). An agent can distinguish this from list_plans (domestic plans) without opening either schema, because the description explicitly frames it as the international catalogue feeding pay_bill with service: INTERNATIONAL.

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 an explicit prerequisite ('ALWAYS call this before pay_bill with service: INTERNATIONAL'), an explicit anti-pattern ('never guess' the identifiers), and the alternative path for unsupported cases (flexible-amount plans must be completed in the AbaPay app). This is about as complete as when-to-use guidance gets.

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