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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is handled. The description adds genuinely new behavioral context: the tool returns a single profile only (not ownership/officers/accounts) and enumerates what the returned object contains. It does not mention rate limits or failure behavior for unknown ids, keeping it short of a 5.

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?

Purpose and input format are front-loaded in the first clause, and the two long sentences each carry distinct payload (return shape vs. sibling routing). The return-value sentence is dense but justified because there is no output schema; a small amount of parenthetical nesting costs it a perfect score.

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 fully compensates by enumerating the return fields (id, title, url, text, metadata) and the contents of the enriched JSON profile. Combined with the sibling routing, an agent has everything needed to select and call this tool correctly.

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 coverage is 100% and there is only one parameter, so the schema baseline already applies. The description still adds value by documenting an alternative accepted form ('company:<number>; a bare company number also works') that the schema example alone does not make explicit.

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 ('Fetch one UK company by an id from search') and even specifies the domain ('UK company'). It distinguishes itself from most siblings by naming which ones handle ownership, officers and accounts, though it never addresses the near-identically named sibling get_company, leaving a real ambiguity.

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?

Explicitly routes the agent elsewhere for adjacent needs: 'use get_bundle, get_psc, get_directors or get_financials for ownership, officers and accounts,' and scopes the tool with 'Profile only.' It also clarifies the accepted id form ('a bare company number also works'), so both when-to-use and how-to-call are covered.

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