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

Annotations already mark it as read-only, idempotent, and non-destructive. The description adds genuinely useful behavior beyond that: what makes a card 'added', how isDefault is chosen, and how create_card uses the default card when no connected_card_id is supplied.

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?

Three sentences, each earning its place: one defines the resource, one clarifies default behavior, and one disambiguates from a sibling tool. No wasted or filler wording.

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 zero-parameter read-only tool with an output schema and safekeeping annotations, the description covers all the necessary context: what the cards are, what fields are returned, how defaults behave, and how this differs from list_cards. Nothing meaningful 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?

The input schema has zero parameters and full schema coverage, so there is nothing for the description to clarify in that scope. It still adds meaningful context about the output, especially the isDefault flag's semantic meaning, which goes beyond the bare 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?

Uses specific verb 'List' plus resource 'user's ADDED cards' and defines them as own Visa/Mastercard cards enrolled via create_card's add-card flow. Explicitly distinguishes from list_cards, so an agent can recognize the intended scope right away.

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?

Explains when this tool is relevant by tying the listed data to create_card behavior and update_settings, and explicitly names list_cards as a different tool for issued virtual cards. This gives the agent a clear decision point between the two.

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