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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, openWorldHint=false), so the lower bar applies. The description adds genuinely new context: the result comes back in hours and minutes and in decimal hours, and overnight spans are supported, which is the key behavior an agent would otherwise have to infer.

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?

Front-loaded with a concrete example, followed by the operational sentence and a link. The phrasing 'in hours and minutes, decimal and minutes' is slightly garbled and repeats 'minutes', a small but real bit of waste.

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 two-parameter, read-only, idempotent calculator with no output schema, the description supplies the missing piece an agent needs: the shape of the result (h/m, decimal hours) plus the overnight case. Only the missing comparison to similar time/date tools keeps it short of a 5.

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% and the schema already documents the HH:MM 24-hour format and the next-day rule for reversed times. The worked example in the description reinforces the defaults but adds no new parameter-level syntax or constraints, so 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?

The description states a specific operation on a specific resource: getting the elapsed time between two clock times, with a worked example (9:15 AM to 5:45 PM = 8 h 30 min). The phrase 'clock times' implicitly separates it from date-oriented siblings like date_difference_calculator, but no sibling is named explicitly.

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 implied by 'the time between any two clock times' and the overnight-shift note, which tells the agent this tool handles end-before-start cases. However, it never says when to prefer this over hours_calculator, time_to_decimal_converter, or date_difference_calculator, and gives no exclusions.

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