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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower; the description still adds real behaviour: the exact formula, round-up-to-selling-increment behaviour, unit handling, and the edge case that negative shrinkage means growth. Minor gap: it never states plainly that the returned value is the purchase length.

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?

Two sentences, front-loaded with purpose and immediately followed by the formula that determines the answer. No filler; every clause (unit flexibility, negative shrinkage) carries information the caller needs.

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 pure calculation tool with no output schema and annotations covering the safety profile, the description supplies the formula, rounding rule, unit labelling, and the negative-shrinkage edge case. Only the exact shape of the result is left implicit, which is a small residual gap.

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 already 100%, and the description goes beyond it by showing how the parameters compose — usable length plus extra, divided by one minus shrinkage, then rounded to the shop increment, with the unit used only for labelling. It also flags that a negative shrinkage rate is growth, reinforcing the schema's -100..100 range.

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?

Specific verb and resource: 'Works out how much fabric to buy before washing so that the usable length needed remains afterwards.' The boundary with the sibling measure_fabric_shrinkage is implicit in the pre-wash purchase-planning framing, but the description never names that sibling to make the split explicit.

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 rather than stated — 'before washing' and 'how much fabric to buy' signal the scenario, and 'Works in metres or yards (any one unit)' constrains inputs. There is no explicit when-to-use / when-not-to-use rule and no pointer to measure_fabric_shrinkage as the alternative for the measurement step.

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