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

Annotations already state the tool is read-only, idempotent, and non-destructive. The description adds useful behavioral detail beyond that: it discloses the exact output shape (H:MM clock value, decimal hours, total minutes) and the edge case that results can be negative when subtracting. This is meaningful additional transparency.

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?

The description is three focused sentences: the operation, the output formats, and the negative-result edge case. It is front-loaded with the primary action, includes the source for credibility, and contains no filler or repetition.

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, fully-optional-parameter calculator with an output schema and read-only annotations, the description covers what the tool does, what it returns, and an important edge case. An agent has enough information to select and invoke it correctly without further clarification.

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 every parameter is already documented in the schema. The description reinforces the meaning of the hour/minute pairs and the operation enum, but it does not add new parameter-level meaning beyond restating what the schema provides.

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 clearly states the operation (add or subtract two durations) and the resource (hours and minutes), and it explicitly lists the three return formats. It is specific enough to be recognizable, though it does not explicitly distinguish itself from nearby siblings like hopi_hours_calculator or 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?

The action 'Add or subtract two durations' gives a clear sense of when the tool would be used, and the examples imply this is for duration arithmetic rather than time zone or clock conversion. However, there is no explicit when-to-use versus alternative guidance, and no mention of exclusion cases such as when to prefer another hopi calculator.

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