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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, non-open-world), so the bar is lower. The description adds genuine value by disclosing the shape of the result — days plus weeks/months/years conversions and weekday/weekend counts — which matters because no output schema exists. It still omits edge-case behavior (e.g., reversed dates, end-date-empty meaning today).

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?

Three short sentences, front-loaded with the core result and with the includeEnd option called out before the reference URL. No filler, though the URL is marginally extraneous to tool selection.

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 3-parameter, zero-required, no-output-schema calculator, the description covers the computed outputs and the one behavioral toggle. It is nearly complete; only edge-case semantics and sibling disambiguation are missing, which is acceptable given the rich 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 all three parameters (start, end, includeEnd) are already documented in the schema. The description only gestures at includeEnd via "include the end date" and adds nothing about the date format or the empty-end default. Baseline 3 is appropriate.

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 names a specific computation (days between two dates) plus the derived outputs (weeks, months, years, weekday/weekend counts), which distinguishes it from generic siblings like date_calculator or time_duration_calculator. However, it never explicitly names which sibling to use instead, so the differentiation is implied rather than stated.

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?

"Choose whether to include the end date for event lengths" gives a hint of the use case, but there is no explicit when-to-use statement, no exclusions, and no routing to competing tools such as business_days_calculator or time_duration_calculator. Usage is only implied.

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