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

Annotations already cover safety (readOnlyHint, idempotentHint, openWorldHint=false), so the description's job is to add context — and it does, disclosing that leap years and month ends are handled and that the result includes the weekday. It stops short of saying how multiple units combine or whether the calculation is calendar-based vs. fixed-length months.

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 tight sentences, front-loaded with the capability and an illustrative example. The trailing marketing URL is not strictly necessary for an agent to invoke the tool correctly, which costs it a perfect score.

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?

For a zero-required-parameter, 6-param, no-output-schema tool, the description covers the essentials: what it computes, the units, and edge-case handling. Minor gaps remain — how multiple units combine in one call and the fact that everything defaults (op=add, start=today) — but these are covered in the schema.

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 the schema already documents op, start, days, weeks, months and years including defaults and ranges. The description merely names the units, adding no syntax, combining rules, or explanation of the 'add'/'subtract' op beyond what is structured — the 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?

States a specific verb set (add/subtract), the units involved (days, weeks, months, years) and the output (exact date and weekday), so the core function is unambiguous. However, it never distinguishes itself from overlapping siblings such as date_difference_calculator, day_of_week_calculator or business_days_calculator, which an agent must choose between.

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?

Usage is only implied through the example '90 days from today'; there is no explicit when-to-use statement, no negative cases, and no routing to the many date-related siblings that could plausibly handle a related request. Adequate but leaves selection to inference.

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