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

Annotations only declare readOnlyHint, so the description carries the rest of the burden, and it does: it states the return payload includes deck ids usable by other tools, what each deck teaches, entry counts, and field meanings. That is meaningful disclosure for a lookup tool, though it omits whether the list is static or paginated.

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?

Three sentences, front-loaded with the resource, then the return contents, then the actionable instruction. The deck enumeration is somewhat long but each named domain earns its place by telling the agent this catalog is worth consulting.

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 no input schema and no output schema, the description is the only place return shape can be described, and it covers ids, subject matter, entry counts, and field semantics. A brief note on stability or size of the response would make it complete.

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?

The tool takes zero parameters, so the baseline is 4. Nothing in the description invents or misdescribes inputs, and the note that returned ids are 'the value other tools take' usefully describes how outputs feed other calls.

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?

Names a specific resource (the catalog of K2 study decks) and enumerates exactly what it covers (eight curated datasets across kanji, HSK, Hangul, Spanish, French, Latin). It is clearly distinguishable from search_deck and get_entry, which operate on individual entries rather than the catalog.

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?

Explicitly instructs 'Call this before search_deck,' giving the agent an ordering rule and naming the sibling that depends on it. It stops short of saying when not to call it (e.g., if deck ids are already known), so a 4 rather than a 5.

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