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

Even though annotations already declare readOnly=true and destructive=false, the description adds substantial behavioral detail: results carry provenance (accession number, filing date, exhibit URL), the status distinguishes 'no Exhibit 21' from lookup failure, and the data comes directly from SEC filings. These details meaningfully shape the agent's expectations beyond the annotations.

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?

The core purpose is front-loaded in the first sentence, and later sentences each add meaningful context: example, filter usage, provenance, edge cases, and coverage limitations. It is fairly long and dense, but for a financial-domain tool with legal specifics, the detail earns its place without being bloated.

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?

Given there is no output schema, the description carries the full burden of explaining return behavior, and it does so thoroughly: it describes the subsidiary list, jurisdiction of incorporation, provenance fields, name filtering, absence-of-data handling, and coverage gaps. An agent has enough context to call this tool correctly and interpret its results.

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 100%, so the baseline is 3, but the description adds real semantic value. It clarifies that ticker_or_cik is specifically the PARENT company, explains the name_filter use case as a quick membership check, and describes the source and structure of the data behind the parameters. This exceeds mere schema repetition.

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 opens with a precise, specific definition: 'the REVERSE of sponsor_to_filer' that lists a parent company's subsidiaries from Exhibit 21 of its 10-K. It names the exact SEC source and clearly differentiates itself from the sibling sponsor_to_filer, so an agent can select it unambiguously.

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 explicitly states when to use this tool instead of sponsor_to_filer: instead of making ~10 calls guessing candidate names and confirming each, call this once to get the full subsidiary list. It also documents exclusions (foreign private issuers / 20-F filers not yet covered) and how absence of Exhibit 21 is handled, giving the agent clear decision criteria.

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