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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description's main addition is the exactly-two-inputs constraint, which largely duplicates the schema's oneOf; it says nothing about rounding, precision, or handling of invalid input beyond what structured data provides.

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?

A single front-loaded sentence with no filler. It is efficient, though its brevity leaves gaps that a slightly longer sentence could have closed.

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?

With four simple parameters, an output schema covering return values, and annotations covering safety, the definition is nearly complete. Remaining gaps are minor: precision/rounding behavior and error handling for the exactly-two constraint are unstated.

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 75% and each property is documented (pace format, time format, distance units, enum for units). The description only gestures at 'distance units' and the two-of-three rule, adding little beyond the schema; baseline 3 applies when the schema does the heavy lifting.

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 ('Calculate') and the exact resources (running distance, elapsed time, pace), plus the key constraint that exactly two of the three must be supplied. It is clear what the tool does, though it offers no explicit differentiation from siblings like unit_convert or hours_calculator beyond the tool name.

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 'exactly two values' rule gives a real invocation constraint, but that rule is also encoded in the schema's oneOf. There is no guidance on when to prefer this over related calculators (unit_convert, hours_calculator) or what happens with invalid combinations; usage is implied rather than explained.

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