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

Annotations already establish readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds real behavioral substance beyond that: it discloses the exact failure conditions (ends in ん, already used) and the additional outputs (dictionary membership, required starting kana). It does not mention the loose_dakuten house-rule variant or any error/ambiguity 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?

One dense sentence that front-loads the core check and then appends the secondary outputs. Nothing is padded and there is no filler. It is slightly run-on, with the rule list and the output list competing in a single sentence, but the size is appropriate.

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?

There is no output schema, so the description must carry return semantics, and it does name two of the returned facts (dictionary membership, next required kana) plus the win/lose conditions. It stops short of describing the response shape or how a valid vs invalid move is represented, which an agent calling this programmatically would want.

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 all four parameters are already documented in the schema, making 3 the baseline. The description reinforces the meaning of the `used` parameter ('was already used') but adds no format, syntax, or edge-case detail beyond what the schema states, and never mentions loose_dakuten.

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: it checks whether a proposed word legally follows the previous word in shiritori, and enumerates the rule set (last-kana match, ん loss, reuse loss). That is clear and actionable. It does not explicitly distinguish itself from the sibling check_word, which a reader must infer checks a single word rather than a move pair.

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 only implied by the phrasing 'the next word' and 'this game' – it is clearly a mid-game move validator. There is no explicit when-to-use statement, no mention of when to prefer check_word or suggest_next, and no prerequisites or ordering guidance.

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