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

Annotations already declare readOnlyHint=true, so safety is covered. The description does add genuine behavioral value beyond that by disclosing result ordering (HSK entries first, then shorter words) and the shape of each entry (pinyin, Hán Việt, Vietnamese and English senses, HSK level, per-field src). It does not say whether results are capped by anything other than limit or what happens when no words contain the character.

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?

A single dense sentence that front-loads the core operation, followed by the entry-shape detail. No filler, though the packing of ordering and field list into one sentence makes it slightly harder to scan than two short sentences would be.

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 explaining returns and it does so adequately, listing the fields in each entry and the ordering rule. For a two-parameter read-only lookup, what remains missing (empty-result behavior, typical result volume) is minor.

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 both parameters are already documented in the schema, including the pattern for char and the 1-100 range for limit. The description's phrase 'words of two characters or more that contain a character' reinforces that char is a substring constraint rather than a prefix, which is a small addition beyond the schema, but it adds nothing about limit behavior or default.

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-like operation (return words containing a character) plus concrete scope constraints: two characters or more, simplified or traditional input, and full dictionary entries as output. The 'two characters or more' qualifier implicitly separates it from the single-character sibling get_character, though no sibling is named explicitly.

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?

Usage is implied rather than stated: an agent can infer this is the tool for finding multi-character words containing a given character, and the described ordering (HSK words first, then shorter words) hints at how to interpret results. There is no explicit when-to-use vs when-not, and no routing to alternatives such as lookup or search_meaning.

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