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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description's remaining behavioral content ('Returns: {weeks, months_approx, working_days}') merely restates what the output schema already provides, adding little beyond 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?

Two short sentences, front-loaded with the core purpose and no filler. The return-shape sentence is mildly redundant given an output schema exists, but it is brief and does not bloat the definition.

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 simple, read-only, two-parameter calculator with full schema coverage and an existing output schema, the description covers what is computed and what comes back. Nothing an agent needs to invoke it correctly is missing.

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?

Both parameters are fully documented in the schema (100% coverage, each with type and YYYY-MM-DD format), so the schema carries the burden. The description only says 'between two dates' and adds no format, ordering, or edge-case semantics (e.g. whether end_date is inclusive) beyond what the schema already states.

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 verb and resource ('Calculate days, weeks, approximate months and working days between two dates') and names the exact outputs, so an agent knows precisely what the tool computes. It does not, however, differentiate itself from overlapping siblings such as calculate_working_days, calculate_day_of_week, or calculate_time_difference, which is why this falls short of a 5.

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?

There is no statement of when to use this tool rather than the many other date/duration siblings, and no exclusions. The only routing hint is a vague pointer ('See list_bundles for related temps-rh calculators'), which suggests a bundle rather than a usage condition.

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