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

With no annotations provided, the description carries the full burden of behavioral disclosure. It is transparent about rate limits, quota charges, cached-result behavior, and the exact contents of the returned public record including deadlines and penalties. It does not mention auth or error behavior, but the key operational costs and outputs are disclosed.

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 three focused sentences: what it does, what it returns and costs, and how to obtain the input. Every sentence earns its place, the key action is front-loaded, and the prerequisite instruction is placed as a natural closing call to action.

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 that there is no output schema, the description enumerates the return fields and explains the cost model, which is important context for an agent. It is slightly incomplete regarding the IE/US enum values, since the description and schema mention register access only for GB and AU, leaving the behavior for IE/US unspecified.

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 already documents both parameters with descriptions and examples, and coverage is 100%. The description adds only the mapping that the registered number is either a GB company number or AU ABN, which is useful but only marginal value beyond the schema. Baseline 3 is appropriate.

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: 'Look a company up on its public register' by registered number. It clearly scopes the tool to GB and AU registers and distinguishes it from search_companies by naming the prerequisite, so an agent can tell lookup from search without opening the schema.

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 explicitly instructs 'Find the number first with search_companies,' giving a clear when-to-use and prerequisite. It also notes that the tool is rate limited and quota-charged while cached results are free, which directly helps the agent decide when to call this tool versus alternatives.

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