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

No annotations are provided, so the description carries the full burden and adds almost nothing: it does not say what dimensions are compared, whether companies must be UK-registered entities, what happens if a number is invalid, or what the response contains. The only added context is the UK scope.

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?

A single front-loaded sentence with zero filler, and the key constraint (two companies) leads. It is efficient, though its brevity borders on under-specification rather than deliberate concision.

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?

No output schema exists, so the description should explain what a comparison returns (which fields, whose data wins on conflict), but it does not. For a tool whose entire value is the comparison result, this leaves the agent guessing before it calls.

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% – both parameters ('First company number', 'Second company number') are already documented in the schema. The description adds no format, source, or lookup semantics beyond the schema, so baseline 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?

States a specific verb (compare) and resource (two UK companies) with an explicit scope modifier (side by side). An agent can distinguish it from lookup_company, which handles a single company, though no sibling is named outright.

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?

No when-to-use or when-not-to-use guidance is given. The agent must infer from the name and 'two' that this is the multi-company variant rather than lookup_company or search_companies; nothing in the text routes it explicitly.

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