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

With readOnlyHint=true already covering safety, the description still contributes real behavioral context: result timestamps are ISO 8601 UTC (add 9 hours for JST) while from/to filters are JST date-only values, and reasons are machine-classified. It omits return shape, ordering, and whether the 50/100 limit implies pagination, so it stops short of full disclosure.

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?

Purpose and scope are front-loaded correctly, but the English/Japanese duplication inflates the text and the promotional line 'Corporate-event data no competing Japanese API exposes' does not help an agent decide or call. The timezone rule is stated effectively twice before the JST filter clarification is added.

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?

For a read-only, filter-only feed with no output schema, the description covers what is returned (classified extraordinary-report events), the filter axes, and the timezone semantics needed to interpret both inputs and outputs. Remaining details like default ordering are minor.

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 coverage is 80%, so a baseline of 3 would apply, but the description adds a genuinely non-obvious constraint: from/to are Japan-time dates even though the payload timestamps are UTC. Combined with the reason-key examples and sibling list tool in the schema, the parameters are well understood.

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 resource (EDINET 臨時報告書 / extraordinary reports), what it delivers (a feed with machine-classified reasons), and enumerates the reason classes. This clearly separates it from siblings like get_events_feed or get_disclosures, so an agent can pick it without opening the 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?

The description gives scope options — 'Query by company or across the whole market for a date range' — which implies how to call it, but never states when to choose it over get_disclosures, get_events_feed, or get_extraordinary_report_reasons, nor any exclusions. The pointer to the reasons sibling exists only in the schema, not the description.

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