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

Annotations already declare readOnly, non-destructive, and closed-world, so the safety profile is covered. The description adds value beyond them by disclosing the return shape (owned/total ratio) and an eligibility constraint, though it does not say what is returned for a set the user owns nothing in.

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 short sentences, zero filler, and the eligibility constraint is front-loaded before the clarification of the return value. Nothing redundant relative to the annotations.

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 read with annotations carrying the safety profile, the definition covers purpose, eligibility, and the nature of the result. The unexplained language parameter is the only real gap, and a missing output schema is partly offset by the 'owned/total' hint.

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 50%: setSlug is documented in the schema, but language is undocumented in both schema and description, and the description does not compensate with any language or slug-format guidance. With one of two parameters effectively covered by the schema, the baseline of 3 applies.

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 names the specific computation (set completion, owned/total) and the required precondition (the user already collects the set), which makes it distinguishable from collection_summary and portfolio_analysis. It is a noun phrase rather than an explicit verb, but the resource and output are unambiguous.

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 gives a real gating condition (at least one owned card or wishlist item in the set) and implicitly steers away from the priced valuation path by stating it is 'not a priced dump'. It does not name a specific alternative sibling to use instead, which keeps it short of a 5.

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