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

Annotations cover the safety profile (readOnly/no destructive/openWorld), and the description goes well beyond them: it discloses the exact return payload (word order, dictionary pinyin, short meaning, HSK level, per-HSK-level counts) and warns that pinyin is the dictionary reading rather than a sentence-specific one. That caveat is exactly the kind of behavioral trait an agent cannot get from structured fields.

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?

Four short sentences, front-loaded with the action and the return shape, ending with the usage boundary. No filler, no restatement of the title, and every sentence carries information an agent needs.

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 present, the description carries the return-value burden and does so fully (per-word fields plus HSK-level counts), while annotations handle the safety profile. Nothing material for correct invocation appears to be 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?

Only one parameter and schema description coverage is 100%, with maxLength/minLength already documented in the schema. The description adds only the loose framing of 'sentence or short passage' and no syntax, encoding, or format guidance beyond what the schema states, so the baseline 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?

Specific verb + resource: 'Split a Chinese sentence or short passage into words.' It also frames the boundary against a plausible competing intent ('Do not use it to translate a whole passage'), which differentiates it from translation-oriented behavior an agent might otherwise assume.

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?

Gives two concrete use cases ('gloss a sentence word by word', 'judge how hard a text is') and one explicit exclusion ('Do not use it to translate a whole passage'). It stops short of naming a sibling tool (e.g. lookup_word, search_dictionary) as the alternative, so routing between siblings still requires inference.

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