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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds real value by naming the computed outputs (income tax, National Insurance, student loan, amount left to pay, take-home) and the PAYE offset, but says nothing about the tax-year defaulting behavior or any assumptions such as England/Wales vs Scottish rates.

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 dense sentence with the scope front-loaded and the income sources and outputs packed into parenthetical and colon lists; nothing is redundant. The trailing colon list of outputs is slightly awkward to parse but costs no extra length.

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 nine optional parameters and no output schema, the description carries the burden of telling the agent what comes back, and it does so by naming the five result components. It omits any note on pension contributions affecting the result or on rate-region assumptions, which are the remaining gaps for a tool of this complexity.

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 100%, so every parameter is already documented, and the description largely mirrors those fields (employment, self-employment, rental profit, dividends, savings interest, PAYE). It adds no meaning for pensionContributions, studentLoanPlan or taxYear beyond what the schema states, so baseline 3 applies.

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 ("Calculate the combined UK tax") and enumerates exactly which income sources are combined, which implicitly separates it from single-source siblings such as calculate_dividend_tax or calculate_rental_income_tax. It never names an alternative tool, so differentiation is inferred rather than stated.

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 phrase "income from several sources in one tax year" implies the usage condition, and "allowing for PAYE tax already deducted" hints at a scenario. There is no explicit when-not guidance and no pointer to the single-source calculators for simpler cases, leaving the agent to infer routing.

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