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

Goes well beyond the annotations: discloses that credit is spent immediately, that the operation cannot be reversed, that idempotency_key makes retries safe (particularly useful given idempotentHint=false), and that it returns per-number status plus requestId. Annotations already flag destructiveHint, but the description supplies the operational consequences.

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?

A single dense paragraph with the write-risk warning and the credit-spend caveat front-loaded, followed by prerequisites, currency semantics, retry guidance, and return shape. Every sentence carries information; the endpoint string is the only arguable 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?

For a destructive, non-idempotent financial mutation with no output schema, it covers the safety gate, reversibility, idempotency, currency units, batch limit, return shape, and follow-up path. Nothing an agent needs before invoking it 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 67%; the description adds meaning the schema lacks, notably that amounts are denominated in the given ISO currency and gives examples (KES, UGX, TZS) where the schema only has an uppercase-3-letter pattern. The idempotency_key and confirm semantics largely restate what the schema already documents well.

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 ('top up mobile airtime') with an explicit scope (up to 25 phone numbers) and a WRITE marker, which cleanly separates it from send_sms, send_mobile_data, and read-only siblings like get_balance.

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 a concrete precondition for calling (confirm=true only after the user approved each number and amount) and routes follow-up to africastalking_find_airtime_transaction. It does not explicitly distinguish when to pick this over send_mobile_data, but the resource difference makes that reasonably clear.

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