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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, and the description adds real domain context beyond them: what a licence does and does not imply ('each job still has to qualify'), that register entries are legal names, and that register data carries an OGL attribution. It does not cover failure modes (e.g., no match, rate limits), so it stops short of 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?

Front-loaded with the core question and the lookup mechanics, and every sentence carries information. Minor waste: the opening sentence restates the title verbatim, and the OGL licence sentence is boilerplate rather than agent-useful.

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 compensates by enumerating the returned fields (town, licensed routes, register date) and by scoping the tool to UK sponsorship only. Nothing an agent needs to call or interpret this tool correctly 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?

Single parameter with 100% schema coverage, so baseline is 3; the description adds genuine value by framing the input as a legal-name lookup and warning that brand names may miss, which the schema's example alone does not convey as a retry strategy.

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+resource: looks up an employer in the UK Home Office register of licensed sponsors, and names what it returns (town, licensed visa routes, register date). It is clearly distinguishable from siblings like check_salary, company_lookup, or check_job_link.

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?

Gives concrete trigger phrasings ('does Deliveroo sponsor visas?') and an explicit boundary rule: for US jobs, use the visa_sponsorship field on search results instead. It also supplies a fallback strategy (try the legal name if the brand name is not found).

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