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

With no annotations, the description carries the full burden and does disclose real behavioral traits: results carry provenance and a retrieval timestamp, and responses may be cached for up to 24 hours, so the agent knows data can be stale. It omits auth requirements, rate limits, and error/empty-result behavior, which keeps it from a 5.

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?

Two sentences, front-loaded with the action and resource, then the return shape and freshness caveat. Every clause carries information; the return-field list is long but justified because there is no output schema.

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 usefully enumerates return fields and notes caching and provenance, which is what an agent needs to interpret results. Missing pieces are authentication, rate limits, and the distinction from the sibling profile tool, so it is strong but not fully complete.

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 ('q' as company name or number, 'limit' as max results) are already documented in the schema. The description adds only marginal meaning, restating the name-or-number duality of 'q'; the baseline of 3 applies.

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?

The description opens with a specific verb and resource: 'Search the UK Companies House register by name or number.' It also enumerates the returned fields (number, status, type, incorporation date, registered address), so an agent knows exactly what it gets. It does not distinguish itself from the sibling uk_company_profile, which is the plausible search-vs-detail alternative, so it falls short of a 5.

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 phrase 'Primary source with retrieval timestamp; cached for up to 24 hours' implies this is the canonical/preferred lookup, which is weak usage guidance. However, there is no explicit statement of when to use this versus uk_company_profile or cross_registry_resolve, and no exclusions or prerequisites are given.

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