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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered; the description adds genuinely new operational context in the error contract (400 invalid number, 404 not found) and the paid-call requirement (x402, $0.005 USDC per call), which an agent must know before invoking. It omits rate limits and response/latency behavior, but the additions are meaningful.

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 action and identifier, followed by the payload of returnable fields, then usage, errors and price — each element earns its place. The field enumeration is long but directly substitutes for the absent output schema, so the length is justified rather than 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 takes on the burden of describing returns and does so field by field, plus error codes and the payment model. Nothing material an agent needs to call this correctly – input, outcome, failure modes, cost – 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 100% for the single 'number' parameter, and the schema already supplies the format example and the leading-zeros note. The description only restates 'by company number', adding essentially nothing beyond the schema – baseline 3 for a fully documented parameter set.

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 ('Check a UK company on the official Companies House register by company number') and enumerates exactly what is returned (name, status, type, incorporation date, address, SIC codes, accounts, charges, insolvency, directors). It is unmistakably distinct from every sibling tool, all of which concern file/web/audio conversion or postcode and website checks.

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 explicit use cases – supplier checks, due diligence, confirming a business is real and active – which sets the intent clearly. It does not name a when-not condition or an alternative, but no sibling operates in this domain, so there is no real competing tool to route away from.

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