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

Annotations already establish readOnlyHint=true, destructiveHint=false and a closed-world computation, so safety is covered. The description adds genuine value by naming the modelled components (deemed employment payment, employer National Insurance, limited company route) and by warning that it is a pay comparison, not a status verdict.

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?

Two tight sentences, front-loaded with the comparison itself and closing with the important scope limitation. No filler and every clause carries information about inputs or scope.

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 read-only calculator with full schema coverage and annotations carrying the safety profile, the description covers the what, the inputs, and the scope boundary well. With no output schema, a brief note on what the comparison returns (e.g. per-scenario take-home figures) would close the remaining gap.

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 including taxYear's enum and the cost/expense optional fields is already documented in the schema. The description mentions day rate and working days but adds no format, default, or range semantics beyond what the schema supplies; 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 (compare) and a precisely scoped resource: inside-IR35 take-home versus outside-IR35 via limited company. It names the computation inputs (day rate, working days, tax year) and explicitly delimits scope by saying it does not decide IR35 status, so it is distinguishable from siblings like compare_limited_company_and_sole_trader.

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 clear context for when the tool applies (contractor pay comparison across IR35 regimes for a given tax year) and an explicit non-use boundary (doesn't determine IR35 status). It doesn't name a specific alternative sibling to route to for status determination, so it stops short of full when/when-not routing.

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