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

Annotations only cover readOnlyHint and openWorldHint; the description goes well beyond by disclosing the pricing model ($0.003 USDC per successful call via x402 on Base/Solana/Arc, failed calls free) and licensing (Crown copyright, OGL v3.0). It also bounds the response contents (max 20 officers, max 10 PSCs, last 10 filings), which materially shapes expectations for a paid call.

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 purpose, then the input options, then the returned fields, then cost/licensing. Every sentence carries information, though the dense field enumeration in the first sentence runs long and the copyright line is arguably secondary for tool selection.

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, so return values need not be explained, yet the description still summarises the record shape usefully. Combined with the disclosed payment mechanics and input forms, an agent has everything needed to invoke it correctly; the only omission is sibling routing, which affects usage rather than completeness.

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 description coverage is 100%, so both parameters are already documented, giving a baseline of 3. The description restates the number-vs-name duality and the "best match plus up to four alternatives" behaviour, which mirrors rather than extends the schema ("best match, up to 5 candidates"), adding no syntax or format detail.

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+resource ("A UK company from Companies House, by number or name") and enumerates the exact payload (status, incorporation date, officers, PSC, filings). It is clearly distinguishable from siblings like company_registry or uk_insolvency by naming the UK Companies House source and its record shape.

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 tells the agent how to choose an input form ("by number (00445790) or name (best match plus up to four alternatives)"), which is real guidance. But it never says when to prefer this over company_registry (pan-registry lookup) or uk_insolvency, nor any precondition such as requiring a valid Companies House number. Usage is implied, not stated.

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