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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the bar is lower. The description still adds substantial domain behavior: explicit handling of ー and small kana under shiritori rules, and detection of words ending in ん, which tells the agent how the lookup differs from a plain dictionary check.

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 front-loaded sentence enumerating the outputs with no filler; the parenthetical about ー and small kana is a tight, necessary qualifier. It is dense rather than padded, though the list format runs long for one sentence.

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 takes on the burden of explaining returns and does so thoroughly (membership, reading, first/last kana, ん flag, next starting kana). What remains missing is input format guidance and any routing relative to the sibling tools.

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?

One parameter with 0% schema description coverage, and the description says nothing about the accepted input form (kanji, kana, romaji, case, length). For a tool whose entire logic hinges on kana, leaving the input format unstated is a meaningful omission that the schema does not compensate for.

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 (look up) and resource (a word) and enumerates exactly what is computed: dictionary membership, reading, shiritori kana, ん detection, and the required next starting kana. It is clearly distinguishable from suggest_next and check_move by its output set, though it never names those siblings 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?

No when-to-use, when-not-to-use, or alternative routing is given. An agent cannot tell from the description whether this should be called before or instead of check_move or suggest_next, which is a real gap given the shared shiritori domain.

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