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

With no annotations, the description carries the full burden. It usefully discloses the UK-only scope, the weekend/bank-holiday skipping behavior, and a 1-credit cost, but says nothing about the default division when omitted (presumably england-and-wales), error behavior for invalid dates, or what result type is returned.

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 covering both modes, the skipping rule, and the cost note. No filler; every clause carries information.

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 calculator-style tool with no annotations and no output schema, the description should clarify the return shape (an integer count versus a YYYY-MM-DD date) and the mutual exclusivity of 'to' versus 'addDays'. Those gaps leave the agent guessing about the response.

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% but the schema text is thin ('number' for addDays, no default for division). The description compensates by redefining addDays as a count of working days rather than calendar days, which is real added meaning, though the division parameter's region options and defaults go unaddressed.

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: computing UK working days, with the two supported modes spelled out (count between two dates, or offset by N working days). It clearly distinguishes itself from the bank_holidays/public_holidays siblings by noting weekends and bank holidays are skipped, though it never names those siblings explicitly.

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 two operational modes are described, which implicitly tells the agent when each applies, but there is no explicit guidance on choosing this over bank_holidays/public_holidays, and no statement about which mode is chosen if both 'to' and 'addDays' are supplied.

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