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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds context those fields cannot express: no charge is created, no hosted payment URL is returned, and the call requires the 'account-read' scope. The auth requirement and the explicit statement of what is NOT returned are exactly the kind of disclosure an agent needs before calling.

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?

Four short sentences, front-loaded with the read-only constraint, then the no-URL caveat, then the ID requirement and remedy, then the scope. Every sentence carries information an agent would otherwise have to discover through failure.

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?

With an output schema present, return values need no explanation. Given a single required parameter, annotations covering the safety profile, and this description covering provenance, fallback, scope, and what is not returned, an agent has everything needed to call it correctly or route the user elsewhere.

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 earns extra by clarifying provenance ('from the original top-up confirmation') and by excluding a plausible wrong input ('not an invoice/payment ID') – a disambiguation the schema's 'returned when the request was created' wording does not make explicit enough to prevent a mismatched-ID lookup.

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 ('read verified state for an existing top-up request') and immediately scopes it against write operations ('without creating a charge'). It implicitly separates itself from list-style siblings by declaring 'It cannot list top-ups', but never explicitly contrasts with the closest sibling, check_balance, so the reader must infer that boundary.

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 explicit when-to-use (an existing top-up request whose ID you hold), explicit when-not-to-use ('cannot list top-ups'), a concrete alternative when the prerequisite is missing ('ask the account owner to review Account → Billing'), and a fallback for customer action. Nothing is left to inference.

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