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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description's 'Read-only' adds little. It does add the behavioral context that the result is a summarized spend figure relative to a limit, but it does not clarify period boundaries, pending transaction treatment, or other operational details.

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 description is short and front-loaded, with the core behavior in the first sentence. 'Read-only.' is slightly redundant with the annotations, so it is not entirely zero-waste, but overall it is appropriately sized.

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 simple read-only tool with one parameter, an output schema, and safety annotations, the description covers the essential purpose and a practical use case. The main gap is that 'over a period' is vague; it does not explain how the period is determined.

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%, with cardId documented as a UUID value wrapper. The description does not discuss cardId or how it maps to the returned data, so it adds no meaning beyond the schema; the high coverage keeps this at baseline.

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 states a specific verb and resource: it returns how much has been spent on a card over a period against its limit. This distinguishes it from card_get_card, card_get_list_cards, and card_update_card_spend_limit among the siblings.

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 gives an explicit use case: answer 'how much is left on this card' without manually summing transactions. It does not name alternative tools or exclusion conditions, but the intended context is clear.

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