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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuine behavior beyond that: the midnight-wrap rule ('an end at or before the start counts as the next day') and the return shape (hours, minutes, decimal hours). It stops short of error conditions or input validation behavior, which keeps it at 4 rather than 5.

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 the purpose, then the midnight rule, then the return, then sibling routing — a sensible order with no filler. The middle sentence is dense but every clause carries information; only the parenthetical example is arguably redundant with the parameter descriptions.

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?

A two-parameter, read-only calculation tool with an output schema and full annotation coverage needs exactly this much: purpose, the one ambiguous edge case, the return units, and sibling disambiguation. Nothing an agent needs in order to call 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?

Schema coverage is 100% and both params already explain the 0630 / 06:30 forms, so the baseline is 3. The description adds real meaning on top by spelling out the wraparound interpretation and giving a concrete 2200→0630 example, which is the one semantic an agent could plausibly get wrong.

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+resource ('find how long a shift or interval lasts between a start and an end in military time') and immediately scopes it with a worked example (2200 to 0630 = 8h30m). It distinguishes itself from military_time_convert and time_duration_between by name, so an agent can route correctly without opening a schema.

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?

Explicitly names both alternatives and the exact conditions that select them: military_time_convert for translating a single time, time_duration_between when dates differ or a DST time zone is involved. This is a clean when-to-use / when-not-to-use split.

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