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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so safety is covered structurally. The description adds the corpus provenance ('Counted over GraphChinese's 145 graded readings'), which is meaningful context for interpreting the frequency data, though it says nothing about pagination limits or result-set bounding behavior.

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 and its return shape before the usage routing. The enumeration of returned fields is dense but every element carries selection value; only minor tightening is possible.

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 return-value burden and does so completely, enumerating item fields and the summary coverage thresholds. Combined with full annotation coverage and 100% schema coverage, an agent has everything needed to call and interpret this tool.

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 count and offset are already fully documented in the schema, making 3 the appropriate baseline. The description adds no syntax or interpretation detail for these parameters beyond what the schema provides; the 50/80/90/95 percent figures describe output, not inputs.

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?

States a specific verb+resource ('List the most frequent Chinese characters') plus the exact ordering and per-item fields returned (pinyin, meaning, HSK level, cumulative coverage share). It also names a sibling it is not (lookup_word), so an agent can route without opening a schema.

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 the explicit trigger condition ('when the user asks which characters matter most or how many they need') and an explicit exclusion with the correct alternative ('Do not use it for one character's meaning (use lookup_word)'). Both when-to-use and when-not-to-use are covered.

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