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

The description goes beyond the annotations by explaining that the tool 'looks nothing up on any account,' the estimate is purely 'arithmetic on the date supplied,' and it 'does not fetch live data or change accounts.' This aligns with readOnlyHint=true and destructiveHint=false while adding meaningful context about the operational scope. It also explains the regulatory 21-day grace period, which clarifies the estimate logic.

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 a single three-sentence block that front-loads the primary usage. Every sentence carries functional information, but the aside about being 'the one most people have never been shown' is promotional and not needed for tool selection. It is reasonably concise and well ordered.

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?

The description covers what the tool returns, when to use it, the arithmetic basis of the estimate, and clear operational boundaries (no live data, no account changes). With an output schema present, it does not need to enumerate return fields. An agent has enough context to select and invoke the tool correctly.

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%: both issuer and dueDate have detailed descriptions in the input schema. The tool description restates that dueDate produces a derived estimate and that issuer only tailors wording, but it adds little new parameter-level meaning beyond what the schema already provides. Baseline 3 applies.

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 the tool's function: it returns the ways to find a Canadian credit card's statement closing date and derives an estimated closing date from a payment due date. The opening 'Use this whenever someone does not know their statement closing date' names a specific use case, and the phrase 'the date every other tool here depends on' helps distinguish it from 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?

The first sentence explicitly gives trigger conditions: 'Use this whenever someone does not know their statement closing date, or gives a payment due date and asks what to pay.' It also states what the tool does not do ('does not fetch live data or change accounts'), which helps rule out inappropriate use. However, it does not name alternative sibling tools or give explicit when-not-to-use conditions beyond those implicit in the description.

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