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

Annotations only declare readOnlyHint/openWorldHint, but the description adds substantial operational context: billing ($0.02 via x402 or API key), that it consumes 2 calls against a quota, the exact field set returned including per-item source_url, and the caveat that vat_number is accepted but unchecked. This is well beyond what the annotations convey.

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-loads the core purpose and keeps everything in a compact block, but the dense comma-separated field enumeration makes it a single heavy run-on. Every element is load-bearing given there is no output schema, so little could be cut.

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 still discloses the return contents, the source_url tracing, the cost/quota implications, and the scope exclusions. An agent has everything needed to decide and call it correctly.

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% and the schema already defines company_number format examples and flags vat_number as unvalidated, so the description largely restates structured data. Baseline 3 applies when the schema carries the parameter burden.

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?

Opens with a specific verb+resource ('Sourced check of a UK company from Companies House') and then enumerates exactly what is checked: status, incorporation date, registered office, SIC codes, filing health, insolvency/charges flags, officers and PSCs. An agent can distinguish this immediately from search_uk_company (lookup) or get_rate-style siblings.

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 exclusions ('Not a credit check, sanctions or PEP screening') and warns that the VAT portion is not yet functional, so the agent knows when this tool is the wrong choice. It does not name a sibling alternative directly, though the company_number schema points to search_uk_company for discovery.

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