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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the no-argument mode returns a 30-item topic/slug list, and the normal mode returns pinyin, meaning and HSK level per word.

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 tight sentences, front-loaded with what the tool returns, then the zero-argument discovery mode, then the inclusion/exclusion rule. No sentence is filler.

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 output schema, the description carries the burden of describing return values and does so (pinyin, meaning, HSK level). Annotations cover the safety profile, and the single optional parameter's dual behavior is explained, leaving no material gap for correct invocation.

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 100%, so the baseline is 3; the description goes slightly beyond by spelling out the no-topic behavior (30 topics and their slugs) and reinforcing that topic is a slug-like selector. It still does not clarify the slug pattern or max length beyond what the schema already documents.

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 states a specific verb and resource ('Get the core Chinese words for a topic') plus the concrete return fields (pinyin, meaning, HSK level) and example topics. It also differentiates itself from the dictionary-style siblings by excluding translation of a specific word.

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 clear when ('the user wants words for a situation or subject'), a clear when-not ('Do not use it to translate a specific word'), and a discovery path ('Call it with no topic to list the 30 topics and their slugs'). The alternative tool for single-word translation (lookup_word/search_dictionary) is not named explicitly, so routing still requires mild inference.

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