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

Although annotations already declare readOnly, idempotent, and non-destructive behavior, the description adds valuable context: the catalogue is real and live, only currently purchasable plans are shown, and exact IDs must be reused. It also discloses the fixed-price vs flexible-amount payment constraint, which goes beyond the annotation hints.

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 description is longer than typical but every sentence carries substantive instructions: the browsing order, the mandatory pre-call relationship, and the payment eligibility constraint. It is front-loaded with the 'REAL, live' qualifier and the one-level-at-a-time mechanic, and there is no filler.

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?

Given no output schema, the description compensates by naming exactly what each level returns (countries, product types, operators, plans with codes, foreign price, NGN cost). It also covers the full parameter progression and the integration constraint with pay_bill, so an agent has everything needed to use the tool 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?

The input schema already documents all three parameters with 100% coverage. The description reinforces the hierarchical drill-down order and the need to pass back exact values, but it doesn't add new format or semantic details beyond what the schema provides, so the schema-heavy baseline of 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?

The description clearly identifies the tool as a browser for the live international top-up catalogue, with a specific verb (browse) and resource, and explains the level-by-level traversal. It also distinguishes itself from pay_bill by explicitly stating it must be called before international bill payments.

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?

Provides explicit when-to-use instructions with a mandatory call sequence ('ALWAYS call this before pay_bill with service: INTERNATIONAL'), what each parameter does when omitted, and a clear exclusion: flexible-amount plans cannot be paid via pay_bill. This is direct, actionable guidance with no ambiguity.

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