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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds useful context by specifying the input is a Companies House number and that output includes both a record and a ready-built ownership graph, going beyond the schema.

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?

The description is a single sentence that front-loads the scope ('UK company'), the key input ('Companies House number'), and the output. Every element carries meaning with no waste.

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?

Given the single parameter, supportive annotations, and straightforward lookup nature, the description covers the core workflow adequately. It does not detail the ownership graph structure or error behavior, but for this simple tool the level is sufficient.

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?

The schema only defines 'number' as a string with no description, and coverage is 0%. The description compensates by identifying it as a Companies House number, giving the agent the essential semantic needed to invoke the tool correctly.

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 clearly states the tool returns a UK company record and a ready-built ownership graph for a Companies House number. It distinguishes itself by the specific identifier type and the ownership graph output, though it does not explicitly name sibling tools.

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 description implies use when you have a UK Companies House number, which narrows the context. However, it gives no explicit guidance on when to prefer this over siblings like lookup_by_identifier or get_company_details, and does not state exclusions.

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