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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the lower bar applies. The description does add real value beyond them by describing the return content's markup conventions (furigana in 《…》, wakachi-gaki spacing) and the provenance of source links, but it says nothing about behavior on a missing or invalid ID.

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?

Two sentences, front-loaded with the verb and resource, then the payload contents, then the prerequisite. No filler and no repetition of the title or annotations.

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 carries the burden of explaining return values, and it does so concretely (Markdown body, term explanations, source links, last_verified). The only gap is the absence of any statement about error/empty results for an unknown ID.

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?

With 100% schema description coverage on a single 'id' parameter, the schema already documents the expected slug. The description adds only the provenance hint that IDs come from list_documents, which is genuine but marginal, so the baseline 3 is appropriate.

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 and resource ('Get one Easy Japanese document by ID') and immediately enumerates what the payload contains: Markdown body with furigana markup, term explanations, verified primary-source links, and a last_verified date. An agent can distinguish this from list_documents or search_terms without opening any 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?

'Use list_documents first to find the ID' gives an explicit prerequisite and routes the agent to the correct sibling for discovery. It does not say when *not* to use this tool (e.g., bulk retrieval or searching by term), so it falls short of full when/when-not guidance.

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