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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds that results are expressed in meters and 50g/100m balls, but since an output schema exists this largely restates the structured data rather than disclosing new behavior.

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 tightly written sentences, front-loaded with purpose before the cross-reference. The explicit 'Returns: {...}' clause is mildly redundant given the output schema, but costs little.

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 two-parameter, closed-enum calculator with an output schema, the definition is largely sufficient. The gaps are minor: no parameter explanation and a vague bundle reference.

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 0%, so the description carries the burden for the two parameters, and it says nothing about them. The enum values (scarf/hat/sweater/blanket/socks, S/M/L) are self-documenting, but the description adds no meaning about what size refers to or how it affects the calculation.

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 and resource ('Calculate yarn needed for a knitting project') and pins down the output units (meters and 50g/100m balls), which separates it from nearby textile siblings like calculate_fabric_needed and calculate_fabric_yarnage-style tools. An agent can identify the domain without opening the 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?

It points at list_bundles for 'related textile-mode calculators', which is a weak routing hint rather than a when-to-use rule. There is no guidance on when to prefer this over calculate_fabric_needed or calculate_recipe_scaling, and 'textile-mode' is unexplained jargon. Usage is only implied.

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