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

With no annotations, the description carries the full burden and does so: idempotency, per-payment_id 5s throttle, a 30/hour-per-key cap degrading to once a minute, the throttle error_code verify_rate_limited with retry_after, and the credit-your-key side effect. Return shape (verified true/false with a reason) is also disclosed, which is essential since no output schema exists.

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 core action and its side effect are front-loaded in the first clause, and every following clause carries operational information. The nested parenthetical rate-limit details make it dense to parse, but nothing is 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 two-parameter polling tool with no annotations and no output schema, the description covers the prerequisite, throttling behavior, error contract, side effect, and return values. An agent has everything needed to call it and interpret the result 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 description coverage is 100%, so both parameters are already documented, and the baseline of 3 applies. The description adds only implicit meaning by referencing payment_id as the throttling unit; api_key is left entirely to the schema.

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 ('Checks on-chain whether an invoice ... has been paid') plus the side effect ('credits your key'). It explicitly ties itself to the sibling create_topup_invoice, so an agent can distinguish it from check_token_risk and the other siblings without opening a schema.

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?

Establishes the prerequisite workflow (must follow create_topup_invoice) and gives polling guidance ('safe to call repeatedly (idempotent), at most once every 5 seconds'). It doesn't name an explicit alternative tool or state a when-not-to-use case, which keeps it just below a 5.

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