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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds valuable domain context beyond the annotations: the applicable tax year and the personal allowance taper behavior, which materially affects results near the taper threshold. It stops short of stating input constraints or assumptions (e.g., England/Wales/Scotland 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?

Three tight sentences, front-loaded with the purpose, then methodology, then returns. The enumerated return fields are largely redundant with the existing output schema, which is minor waste, but nothing else is filler.

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 an output schema present and annotations covering the safety profile, the description needn't explain return values, yet it does. Tax year and methodology are included. What's missing is guidance on regional rate variations (Scotland vs England/Wales) and sibling routing, which would make it fully complete.

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% and the single parameter's meaning (annual gross income in GBP) is fully documented in the schema. The description adds no syntax, format, or edge-case detail for the input, so the 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 with jurisdiction, tax year (2025/26), and calculation method (HMRC progressive brackets with personal allowance taper). This clearly distinguishes it from siblings like calculate_uk_ni_contributions or calculate_uk_council_tax without needing to open a schema.

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?

Usage is implied by the jurisdiction and tax year, and it points to list_bundles for 'finance-uk' calculators. However, it never states when to use this versus other UK tax tools (NI, council tax, student loan) or what inputs are out of scope. Adequate but leaves routing to inference.

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