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

No annotations are supplied, so the description carries the full burden; it does add one piece of real behavioral context by disclosing the 1-credit cost. It does not state what is returned (VAT amount, gross, net?), what rounding is applied, or how the add/extract direction is selected — the includesVat parameter is never explained.

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 compact sentences with zero filler, and the core capability is front-loaded before the credit-cost note. Nothing is repeated or padded.

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 three-parameter arithmetic utility with no output schema and no annotations, the description covers the input rates adequately but leaves the direction-of-calculation logic and the return shape unstated. A caller must guess what comes back and how includesVat changes the result.

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 coverage is 100%, so the baseline is 3. The description does add genuine meaning by mapping 'standard' to 20% and 'reduced' to 5%, which the schema's bare 'standard|reduced|zero|number' does not, but the functionally central includesVat flag remains undefined beyond the word 'boolean'.

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 names a specific verb pair (add or extract) and a specific resource (UK VAT), plus the exact rates handled (standard 20%, reduced 5%, zero, custom). An agent can tell this is a VAT arithmetic tool, though it never names a sibling such as calculate or format_money to sharpen the boundary.

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?

'Add or extract' implies the two directions of use (VAT-inclusive vs VAT-exclusive calculations), so usage is inferable rather than stated. There is no explicit guidance on when to pick this over calculate, nor any prerequisite or exclusion noted.

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