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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered elsewhere. The description adds useful domain context in the UK rate figures, but says nothing about rounding/precision of results or how the two amounts are derived, which is the real behavioral gap for a calculator.

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?

One sentence covering both directions of the calculation plus a short rate note; the primary purpose is front-loaded and nothing is padded. Every clause earns its place.

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?

There is no output schema, yet the description never says what comes back - presumably net, VAT amount and gross figures - nor what precision to expect. For a pure calculator with safety fully covered by annotations, the return-shape omission is the main 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%, with each parameter documented including the mode enum and rate defaults, so the baseline is 3. The description's mention of 20% and 5% largely restates the schema default and adds no new parameter-level meaning.

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+resource pair ('Add VAT to a net price, or remove VAT from a gross price') and names both operating modes, so an agent can tell this is a computation tool rather than the sibling uk_vat_number_checker. It stops short of explicitly referencing that sibling, so it lands at 4 rather than 5.

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 two modes are framed conditionally ('net price' vs 'gross / VAT-inclusive price'), which tells the agent which mode to pick for a given input. There are no named alternatives or exclusions, which keeps it at 4.

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