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

No annotations are supplied, so the description carries the full burden, and it delivers unusually useful disclosure: it distinguishes iXBRL figures as filed from AI-extracted PDF estimates, and warns which fields are reported as filed and that dates are balance-sheet dates. It does not cover error behavior, auth requirements, or read-only/cost implications, but the data-provenance caveat is real value beyond structured fields.

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 front-loaded sentences: identity, return payload, then an accounting-semantics caveat. The final note is narrow but relevant to interpreting the returned figures, and nothing is padded.

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?

With no output schema, the description must summarize returns, and it does so concretely (register details, financials, risk signals, trajectory). Missing only edge cases such as not-found behavior or whether the payload is cached/stale, which keeps it from a 5.

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?

There is a single required parameter with 100% schema description coverage, including a format example, so the schema already does the work. The description adds only the qualifier 'UK' and no syntax or edge-case guidance 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 (look up), resource (UK company), and lookup key (company number), which implicitly separates it from the name-based siblings search_by_name and search_companies. It stops short of naming those alternatives explicitly, so the differentiation is inferred rather than stated.

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 'by company number' phrasing implies you already have an identifier and therefore need this tool rather than a search tool, but the description never states when to prefer it over search_by_name/search_companies or what to do if you only have a name. Usage is implied rather than prescribed.

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