Find yarns for a pattern

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds behavioral context beyond that: results are ranked by number of projects, and the response places user-substituted yarns next to the pattern's required weight/yardage/gauge and the designer's suggestions. It does not discuss result volume or truncation, which is minor given the output schema exists.

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?

It is a single dense sentence, front-loaded with the 'Yarn substitution:' label, and every clause carries information. It is slightly overloaded in the middle with three parallel pieces of data, but there is no padding 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 read-only lookup with a full output schema and full annotation coverage, the description supplies everything an agent needs: what is returned, how it is ranked, and the comparison context. Return-value formatting is handled by the output schema, so nothing material is missing.

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 all four parameters (pattern_id, limit, same_weight_only, include_discontinued) are already documented in the schema. The description says nothing about any of them, including the important same_weight_only filter, so it adds no semantic value above the structured baseline of 3.

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 gives a specific verb and resource: it lists yarns other Ravelry users actually used to make a given pattern. The 'yarn substitution' framing and the detail about ranking by project count make the resource concrete. It never names its siblings (search_yarns, match_yarns, get_yarn_details), so an agent must infer the boundary itself, which keeps it below a 5.

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?

'Yarn substitution' implies the substitution use case, and the mention of the pattern's own weight and gauge suggests a comparison scenario. However, there is no explicit when-to-use versus match_yarns (which sounds like the nearest alternative for gauge-based matching) and no exclusions or prerequisites stated.

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