lookup_company

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

With no annotations provided, the description carries the disclosure burden. It clearly states the input constraint behavior (verbatim number, preserve leading zeros) and the return behavior (company record plus ownership graph with specified edge types). It does not discuss missing-company behavior, but for a lookup tool this is reasonably transparent.

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 with no filler. It front-loads the main action, then provides the key nuance (leading zeros) and representative examples.

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 one required parameter, full schema coverage, and no output schema, the description provides a clear picture of both input and output expectations. It names the graph components, making the tool sufficiently complete for selection and invocation.

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 input schema already covers the single parameter, so the baseline is 3. The description adds meaningful semantics beyond the schema: the number must be passed verbatim, leading zeros must not be stripped, and concrete examples are given. This helps the agent handle real-world Companies House identifiers 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 names a specific verb and resource: 'Look up a UK company by its Companies House registration number.' It also distinguishes itself from siblings by explicitly promising a 'ready-built ownership graph' (officers, PSCs, parent/subsidiary edges), which differentiates it from search_companies or get_company_details.

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 makes the primary use case obvious: pass an exact Companies House registration number. It gives clear input guidance ('Pass the number verbatim — do not strip leading zeros') with examples. It does not explicitly mention when a sibling like search_companies should be used instead, but the context is otherwise clear.

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