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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful behavioral details: handling overnight shifts, subtracting optional break, and returning both hours/minutes and decimal hours. No contradiction.

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?

Four short sentences plus a source URL. The opening sentence states purpose, subsequent sentences cover format, overnight behavior, and output. No redundancy, though the source URL adds marginal value for an agent.

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?

Given a simple 3-param tool with full schema coverage, annotations, and an output schema, the description covers purpose, input format, special edge case, and output format. It omits only minor edge cases like zero duration or break exceeding duration, which are unlikely to harm correct invocation.

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%, so baseline is 3. The description adds interpretive value by clarifying that an end time earlier than start indicates an overnight shift, which is not in the schema's parameter descriptions. It also reinforces the optional break meaning, though that's largely redundant with the schema.

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 ('work out') with a clear resource ('hours worked between start and end time') and adds break handling, time format, overnight special case, and output types. This differentiates it from general time calculators like hopi_time_calculator and converters like hopi_minutes_to_hours.

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?

Provides clear context on when the tool is used – for calculating worked hours with optional unpaid break and overnight shifts – but does not explicitly name alternatives or exclusions. The context is self-sufficient but lacks direct sibling comparison.

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