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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description is not burdened with safety. It adds context about how the estimate is derived (21-day grace period) and transparently disclaims any per-issuer date table, which tells the agent what the tool can and cannot do.

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 four sentences and front-loads the core purpose and distinctiveness. It includes a rationale for the derivation, which is helpful, though the closing clause about being 'more useful than guessing' adds minor value and could be trimmed. Overall, it stays focused and readable.

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?

Given that the output schema exists (per context signals), the description does not need to explain return values. It thoroughly explains the tool's behavior, the derivation logic, the lack of per-issuer data, and when to use it. An agent has enough to correctly invoke this tool and interpret its results.

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%, so both parameters (issuer and dueDate) are already documented with their formats and purpose. The description adds a bit of nuance (issuer only tailors wording, dueDate produces a derived estimate) but essentially repeats what the schema already states, so it meets the baseline without enhancing meaning.

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 a specific verb and resource: 'find the statement closing date for a Canadian credit card.' It also explains the tool's unique value by stating it's the date every other tool depends on and that it can derive an estimate from a due date, which clearly sets it apart from siblings like statement_calendar or when_issuers_report.

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 explicitly states when to call the tool: 'Call this whenever someone does not know their closing date, or gives a due date and asks what to pay.' It also hints that it's better than guessing. However, it does not name alternative sibling tools directly, so the differentiation is implied rather than explicit.

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