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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: data is masked, and full card numbers and vault ids are deliberately withheld, which shapes how an agent should present or reason about the result.

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 tight sentence with zero waste; the key scope ('saved on the wallet') comes first and the privacy constraint follows. Nothing could be removed without losing information.

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 parameters and no output schema, the description does most of the needed work by sketching the return shape (brand, last four) and the empty case. It stops short of saying the result is a collection or how multiple cards are ordered/returned, a minor gap for a display-oriented read tool.

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?

The tool takes zero parameters, so the schema carries the full burden and the baseline of 4 applies. There is nothing for the description to clarify on the input side.

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 clearly identifies the resource: card brand and last four digits of payment methods saved on the wallet, with the empty case ('if any') noted. It lacks an explicit verb ('list/retrieve') and does not distinguish itself from the sibling get_payout_methods, so an agent must infer the split from names alone.

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?

Usage is only implied: an agent can deduce this is the read path for displaying saved cards, and the 'never returned' clause hints it is safe for display contexts. There is no explicit statement of when to call it versus get_payout_methods, or what to do when the wallet is empty.

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