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

No annotations are provided, so the description carries the full burden. It discloses the return contents (registered address, status, incorporation date, officers, filing history), which gives some behavioral insight. However, it does not explicitly state read-only nature, potential side effects, or any required authentication, leaving a moderate gap.

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 two sentences, front-loaded with the core purpose, and every sentence contributes value—the first states what the tool does, the second specifies return items and gives cross-reference to the sibling tool. No wasted words.

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?

For a simple one-parameter retrieval tool with an output schema and clear sibling guidance, the description is complete. It covers what the tool returns, how to use it, and how to find the required input, leaving no significant gaps.

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 provides 100% coverage with a clear description of 'company_number' and an example. The description adds extra context by explaining the purpose of the parameter and how to obtain it if missing ('Use company_search to find a company number by name'), which goes beyond the basic schema definition.

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's function: 'Get the full Companies House record for a company by number.' It names the specific resource (Companies House record) and the input method (by number), and distinguishes itself from the sibling company_search by directing users to that tool for finding a company number by name.

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 explicitly provides usage guidance by referencing the alternative: 'Use company_search to find a company number by name.' This tells the agent when to use this tool (when the number is known) and when to use the sibling tool, offering clear differentiation.

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