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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds value beyond them: the exact status vocabulary (open, awaiting, underpaid, paid, partially_paid, expired) and a polling cadence that implies expected latency/rate behavior. Missing only error behavior (e.g. unknown invoice_id).

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?

Two dense sentences, zero filler: the return contract comes first and the operational advice second. Every clause earns its place and nothing is repeated from annotations or schema.

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 no output schema, the description usefully enumerates the return fields and status values, and the polling/webhook guidance covers the blocking decision an agent faces. Slightly short of complete because nothing is said about failure modes (invalid or expired invoice_id) or whether payment attempts are truncated.

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% and the single parameter already carries the 'invoice_id from create_invoice' provenance note in its schema description. The tool description adds no further parameter meaning, so the baseline 3 applies.

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 ('Returns') and resource ('one invoice'), then enumerates the payload: status with its enum values, pay_url, credit_usd, selected coin, and payment attempts. This clearly separates it from list_invoices (many) and get_payment (a different resource).

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 concrete operational guidance: poll every 15–30 s while the payer pays, or use webhooks instead — naming a real alternative pattern backed by the create_webhook sibling. It lacks explicit exclusions against sibling getters like get_payment, but the usage context is unambiguous.

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