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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, and the description adds real substance beyond that: refunds appear as negative amounts, the response includes total paid, balance still due, payer email, and the online-payment acceptance flag. It doesn't discuss ordering of results or permissions needed, which is why it isn't a 5.

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?

Front-loaded with what is listed and what is returned, then a single sentence on when to invoke it and a short safety tag. Every clause carries information — the refund sign convention and the online-payment flag are non-obvious details, not 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?

With no output schema, the description takes on the job of describing return values and does so concretely: per-payment provider, amount, date, payer email, plus aggregate total paid, balance due, and online-payment capability. For a one-parameter read-only list tool, nothing an agent needs to call it correctly 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?

There is a single required parameter with 100% schema description coverage, and the schema already explains invoiceId comes from list_invoices. The description only indirectly implies the invoice scope ("on one invoice") and adds no format or validity detail, so it matches the baseline for fully documented schemas.

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 gives a specific verb and resource ("List the payments recorded on one invoice") and immediately scopes the content: Stripe/PayPal online payments, their refunds shown as negative amounts, and manually recorded payments. That level of specificity separates it cleanly from list_invoices and list_payment_methods, which cover different resources.

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?

It states concrete triggering questions: whether, when or how an invoice was paid, how much is left, or anything about a refund. That is clear usage context, but it names no exclusions or explicit alternative tools (e.g. use list_payment_methods for available methods), so it stops short of full routing guidance.

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