Card purchases

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, so the safety profile is covered. The description's only addition is "Free," which usefully signals no billing impact, but it says nothing about what is returned, how purchases are ordered or paginated, or the scope of the account data. Minimal value beyond the annotations.

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?

It is short with no wasted words, but the size comes from under-specification rather than tight writing, and the fragmentary phrasing plus the dangling "Free." makes it feel clipped rather than front-loaded.

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 and no return-value discussion, an agent cannot tell what calling this yields — a transaction list, a count, or a total. For a zero-parameter read tool the description should at least state the shape of the result.

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 there is nothing for the description to disambiguate and the baseline of 4 applies. The empty schema makes the parameter story trivially complete.

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?

"Credit purchases made by card on the account" identifies the resource being described, but it is a sentence fragment with no verb, so it is ambiguous whether the tool lists, summarizes, or looks up purchases. It also does not distinguish itself from sibling history tools like carpe_usage_history, carpe_session_spend, or carpe_balance.

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?

There is no when-to-use guidance at all: nothing tells the agent when to pick this over the many other account/history siblings. The word "Free" faintly implies a zero-cost alternative but is not framed as a routing rule.

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