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

Annotations already declare readOnly, idempotent, non-destructive, so the description's safety claims are consistent. Beyond that, it adds important behavioral context: it is a pure calculation engine that does not make payments, change accounts, fetch external data, or retain inputs, and it flags the key modeling boundary that it does not determine future bureau-reported balances.

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 compact but dense, front-loads the trigger phrases, and every sentence carries distinct information. The non-goals list in the last sentence is a single tight clause that prevents misuse without padding.

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 an output schema present, annotations covering the safety profile, and 100% parameter documentation, the description adds the one crucial piece missing from structured data: the boundary between today's balance and issuer-reported balance. Nothing an agent needs to select or call the tool correctly 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?

Schema coverage is 100%, so the baseline is 3. The description still adds high-value semantics by identifying the three parameters that 'drive everything' (limit, statement balance, statement closing date), clarifying the utilization read uses statementBalance, and noting that targetUtilization defaults to one point under 30%. This goes beyond what the schema alone conveys.

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 opens with concrete user intents ('how their cards look, where they stand, which card is the problem') and names the exact outputs: utilization from supplied balances, days to closing date, hypothetical payment to reach target. It also distinguishes itself by explicitly stating it does not determine bureau-reported balances.

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?

The description specifies when to use it ('when someone asks how their cards look, where they stand, or which card is the problem') and gives clear non-goals. It does not explicitly name sibling alternatives like describe_credit_gps or get_credit_plan, but the listed exclusions effectively tell an agent when this tool is not the right fit.

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