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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description goes further by disclosing what is computed and what is returned (net pay per year/month/week, effective and marginal rate, GOV.UK sources), which is genuine behavioral context about output shape and domain coverage. It does not discuss edge cases such as invalid region/taxYear combinations or schema validation failures.

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?

It is a dense two-sentence block that front-loads the core purpose before listing coverage and the alternative-to-manual-calc instruction. Every clause carries information, though the mid-sentence enumeration of tax features is long and could be trimmed slightly.

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 takes on the burden of explaining returns: net pay at three cadences, effective and marginal rate, and source citations. That covers the main gaps for a computation tool with nested params, but the undocumented region and taxYear parameters remain unaddressed.

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 0% across 6 parameters (one a nested object), so the description must compensate. It does name the three pension methods ('salary sacrifice, net pay, relief at source') and mentions student loans and the child benefit charge, mapping to the pension, studentLoans and childBenefitAnnual fields. But it says nothing about region values, taxYear options, or grossSalary units/limits, leaving several parameters undocumented in both places.

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?

The description opens with a specific verb+resource+scope: 'Exact UK take-home pay for one employee', and enumerates the exact deduction categories computed (income tax by band, NI, student loans, pension, 60% trap, HICBC). The phrase 'for one employee' implicitly separates it from the sibling compare_take_home, which presumably handles multiple.

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?

It gives an explicit directive: 'Use this instead of calculating UK deductions yourself', which is clear context for when to reach for it. However, it never names or contrasts with the siblings compare_take_home or get_tax_rates, so the routing decision between the three is left to inference.

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