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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds substantial behavioral context beyond them: partial results are normal, any section may be null for availability or plan reasons, compliance requires a Pro plan, financials are null without machine-readable accounts, and only a missing company yields a 404. It also warns against misreporting nulls as failures — genuine operational guidance not derivable from 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?

Front-loaded with purpose and the sibling-routing rule, then the parameter policy, then error semantics — a sensible ordering. It is dense and fairly long, but nearly every sentence carries distinct information; the null-handling instructions could be tightened slightly without loss.

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 carries the return-shape burden and does so: it enumerates the five sections, explains null semantics, notes ECCTA verification_status is passed through with its own pending-versus-overdue rules, and specifies the single error case. An agent has everything needed to call and interpret this tool.

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 meaning: omitting 'include' returns all five sections, profile is always returned, and non-included sections surface as null rather than being absent. It does not add format guidance for company_number beyond what the schema already provides.

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 with scope: 'Get several views of one UK company in a single request: profile, ECCTA compliance, financials, PSCs and directors.' It then explicitly names the five sibling tools it supersedes (get_company, get_compliance, get_financials, get_psc, get_directors), so an agent can distinguish it without opening any 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?

Gives an explicit preference rule ('Prefer this over calling ... separately') with the rationale (one API call, one credit, one round trip), and states the parameter-selection policy ('Pass include to fetch only the sections you need; omit it to get all five'). No when-to-use decision is left to inference.

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