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

Annotations already declare readOnly, idempotent, openWorld, non-destructive, so the safety profile is covered. The description adds genuine domain context: SIC fields appear only 'when known', individuals and most funds have no SIC, SIC is not GICS, and succession_filing is limited to 8-K12B/8-K12G3 from the last five years.

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 core lookup purpose and well organized into paragraphs by concern. It is somewhat long and spells out return fields even though an output schema exists, which is mildly redundant but still aids interpretation.

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 explains the conditional fields (SIC, fiscal_year_end, state_of_incorporation, succession_filing) that an agent would otherwise misread. Nothing needed to invoke it correctly is missing.

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 0% and the schema is just an untyped string, so the description carries the load: it defines CIK as Central Index Key and gives both accepted zero-padded and unpadded forms ('0000320193' or '320193'). That is meaningfully beyond 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?

States a specific verb and resource ('look up a company by CIK') plus the exact fields returned, and implicitly separates itself from search_companies, which is named as the route for name-based or predecessor-CIK lookups.

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?

Usage is clear: call this when you already hold a CIK, and follow search_companies when the history sits under a predecessor CIK. No explicit exclusion is stated for the name-search case, so it stops just 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.