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

With readOnlyHint/openWorldHint already covering the safety profile, the description earns credit for adding real behavioral context: a one-hop traversal limit, that each relation names its basis field, and the resolution policy that targets absent from the index come back as 'unresolved with reason candidates, never guessed'. That last point is genuinely non-obvious and shapes how the agent should interpret results.

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 purpose before the relation inventory, and the resolution caveat is placed last where it belongs. The middle relation list is dense (seven relation classes in one sentence) but each item is informative rather than padding.

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?

An output schema exists, so return-value shape need not be described, and the description covers the traversal depth, the relation taxonomy, and the unresolved-target semantics that would otherwise surprise a caller. Little is missing for a single-parameter read-only lookup 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% for the single doc_id parameter, so the schema already carries the parameter's meaning and baseline 3 applies. The description adds nothing about doc_id itself — 'parentDocID' refers to returned relation fields, not the input — so there is no uplift above the baseline.

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?

Opens with a precise question-form verb+resource ('How is this EDINET filing related to other filings') and then enumerates the exact relation classes retrieved, which separates it cleanly from siblings like edinet_company_filings and edinet_holdings_tender_offers. The scope qualifier 'One hop each' and the attribution to 'EDINET's document list' make the resource boundary unambiguous.

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?

It implies usage by framing itself as the relation lookup ('How is this EDINET filing related to other filings'), and 'One hop each' tells the agent it will not traverse transitively, which prevents misuse. However, it never names a sibling alternative or states when-not to use it (e.g. use edinet_holdings_tender_offers for tender-offer details rather than relation stubs), leaving routing to inference.

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