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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint), so the bar is lower. The description still adds real behavioral context beyond them: a hard cap of 10 results, relevance ordering, and an empty results array when nothing matches. Those result-set behaviors are not visible anywhere in the structured fields.

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?

Three tight sentences, front-loaded with what it searches, then the return contract, then the next-step chaining instruction. Every sentence carries distinct information: result count limit, ordering, empty-state behavior, and id handoff to fetch. No filler.

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?

With no output schema, the description correctly carries the burden of describing the return shape (results array, id/title/url fields) plus the 10-result cap and ordering. An agent has everything needed to call it and to chain into fetch. Nothing material is missing.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents 'query' fully. The description's phrase 'by name or keywords' restates that semantics without adding format, syntax, or matching rules. Baseline 3 is appropriate when the schema does the heavy lifting.

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 and resource with scope: 'Search UK companies at Companies House by name or keywords.' That is clear, but it does not distinguish itself from the sibling tool 'search_company', which an agent could easily confuse with 'search'. No differentiation language is present.

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 does give forward guidance ('Use fetch on an id to read the company'), which is genuinely useful chaining context. However, it never says when to choose this tool over the similarly named sibling search_company, nor does it state any exclusions or preconditions. Usage is implied rather than defined.

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