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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds real operational context beyond that: flags are "never corrected," ~1% cover disagreement, header-only dates mostly pre-2011, and Q4 has no standalone 10-Q. However it does not disclose result-size or performance characteristics for large windows, and its value here is mostly data semantics rather than tool 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?

Front-loaded with the one-line purpose, then usage, then edge cases, then args – a sensible order with no filler. It is dense and field-name-heavy (irregular_quarter, fy_mismatch, duplicate_report), which costs some readability, but essentially every clause carries information an agent would otherwise have to guess.

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, yet the description still previews the notable return fields and, crucially, their caveats (period_mismatch resolution, transition filings, amendment_only, first). Combined with the exclusions and pagination semantics, an agent has everything needed to call this correctly without further exploration.

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 0%, so the description must carry the load, and the Args block does: cik with an example and a pointer to search_companies, from_date/to_date with an explicit YYYY-MM-DD format, fiscal_year with an example, and limit with its 1-400 range, default 40, and the non-obvious "newest N, returned oldest first" semantics. That last detail is unavailable anywhere in the schema.

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?

First sentence gives a specific verb and resource ("Get a company's fiscal calendar") and immediately defines the unit returned: one row per quarter with its own dates. That scope clearly separates it from siblings like get_financial_history, get_financial_statements, and get_filings, which do not carry fiscal-period dates.

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?

Explicit routing: "Use it whenever a question names a fiscal period" with three concrete query examples, plus the reason alternative guessing fails (fiscal years ≠ calendar years, 52/53-week weekday drift). It also states the exclusion ("10-K/10-Q filers only: a foreign filer (20-F, 40-F) has no quarterly calendar here") and points to search_companies for the CIK.

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