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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add data-shape context — which it does by naming the exact fields returned, including the January 1 vs. card-anniversary reset distinction and enrollment. It does not discuss auth needs, pagination, or result ordering, but for a safe read tool that is a minor omission.

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?

Two sentences, no filler, with the returned-field inventory front-loaded and the usage hint last. It reads a bit like a comma-spliced field list rather than a flowing statement, but every clause carries 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 output schema, the description usefully enumerates the returned fields (value/year, per-cycle cap, cycle, reset rule, enrollment), which is exactly what an agent needs to interpret results. The only real gap is guidance on the required 'card' parameter's expected format.

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 coverage is only 50%: the required 'card' parameter has no description anywhere, and the description only vaguely refers to 'a card' without specifying identifier format (issuer + product name?) or whether it accepts multiple cards. The optional 'country' enum is already fully documented in the schema, so the description compensates for none of the coverage gap.

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 states the resource precisely ('the dollar credits on a card') and enumerates the specific data returned: annual value, per-cycle cap, cycle, reset rule, and enrollment status. The leading 'Only the dollar credits' scopes it away from point/multiplier benefits, though it does not name a specific sibling to contrast with. Clear enough that an agent knows what it gets without opening the schema.

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: 'Use for "when does the X credit reset" questions.' That is a concrete triggering condition rather than an implied one. It stops short of naming alternatives (e.g., credit_deadline_report) or stating when not to use it, so it is strong but not complete routing guidance.

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