Facts and arithmetic for a date

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so no contradiction exists. The description adds meaningful behavioral nuance beyond annotations: 'today' is interpreted as UTC, and month addition uses month-end clamping. These details matter for correct invocation and are not present in the structured fields.

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 dense sentence that front-loads the core outputs and then adds optional operations. Every clause carries distinct information, with no filler or redundancy. It is compact yet sufficiently detailed.

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 the rich input schema, output schema, and safety annotations, the description covers all functional behaviors an agent needs to invoke the tool correctly. It addresses the special 'today' value, the arithmetic semantics, and the days-until calculation. There are no significant gaps for this level of complexity.

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, but the description adds semantic value by explaining behaviorally what the parameters do: '+1 month' with month-end clamping and 'days until another date'. This goes beyond merely repeating parameter names and gives the agent useful interpretation context.

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 a specific set of outputs (weekday, ISO week, day of year, leap year) and optional operations (date addition and days-until), which clearly distinguishes it from sibling tools like world_time or business_days. The title 'Facts and arithmetic for a date' reinforces the exact resource and operation. Nothing is vague or tautological.

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 implies when the tool is useful by enumerating its date facts and arithmetic capabilities, but it never explicitly says when to choose this over sibling tools such as business_days, holidays, or world_time. There are no exclusions or alternative routing hints, so an agent must infer usage from the feature list.

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