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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds value by explaining the calculation contents (personal allowance taper, employee NI) and the return values (gross, tax, NI). It does not mention edge cases or rate limits, but as a stateless calculator this is acceptable.

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?

The description is a single efficient sentence that front-loads the core purpose, then adds specific constraints and outputs. The source URL at the end is extra but unobtrusive. No filler or redundant wording.

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?

Given the two-parameter schema and presence of an output schema, the description sufficiently explains the tool's behavior, scope, and return values. It could mention that it excludes Scotland or student loans, but those are not required for correctness; the description is complete for typical usage.

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?

The schema covers both parameters fully (net, period with enum and default). The description adds only marginal context by mentioning 'yearly or monthly' and 'Amounts in GBP', the latter is not in the schema. With 100% coverage, baseline 3 is appropriate; the description doesn't need to compensate.

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 states a specific verb ('work out the gross salary needed') and resource ('achieving a desired take-home (net) pay'), and narrows scope with tax year, location, and tax code. This clearly distinguishes it from sibling calculators like take_home_pay, which do the reverse (gross to net).

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 provides clear context—2026/27 tax year, England/Wales/NI, code 1257L, and monthly/yearly input—which tells the agent when this tool applies. However, it does not explicitly mention alternatives or when not to use it, though the scope excludes Scotland and other tax years by implication.

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