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

With no annotations, the description carries the full burden. It adds genuinely useful context by disclosing cost ('Flat 30 points per successful run') and by enumerating the returned fields, but it says nothing about authentication needs, failure/not-found behavior, or rate limits. This is a helpfully disclosed simple read, not a fully transparent one.

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?

One tight sentence that front-loads the action and resource, then lists outputs and cost. Nothing is wasted. It is appropriately sized rather than padded.

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 single-parameter lookup tool with no output schema, the description is nearly complete: it names the registry, the accepted input forms, and the fields returned, and discloses the per-run cost. Only the absence of error/edge-case behavior keeps it from being fully 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?

Schema description coverage is 100% and the single parameter already documents its format with an example ('00445790'), so the baseline is 3. The description's 'by registration number or registry URL' merely reinforces what the schema already states, adding no new syntax or constraints.

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 ('Get one company'), the exact resource and registry (United Kingdom, Companies House), and the lookup key (registration number or registry URL). It even enumerates the returned fields. It stops short of naming the sibling run_uk_companies_search, so the lookup-vs-search distinction is implicit rather than explicit.

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 phrase 'by registration number or registry URL' implies the correct usage (single-record lookup when you already have an identifier), and 'Get one company' contrasts silently with a search sibling. But there is no explicit when-to-use/when-not guidance or named alternative, leaving the agent to infer it.

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