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

With no annotations provided, the description carries the transparency burden. It does disclose one meaningful behavioral trait: automatic detection of intra-community B2B reverse charge. However, it doesn't mention return format, potential errors (e.g., invalid category/region), or how missing optional parameters affect behavior. This is partial disclosure, not comprehensive.

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 extremely concise—two sentences, front-loaded with the core action. Every sentence adds value: the first identifies the core calculation and supported regions, the second highlights a key automatic behavior. No wasted words.

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?

The tool has five parameters and no output schema, so the description should provide more operational context. It explains the input dimensions and one behavioral nuance (reverse charge), but it doesn't clarify what the tool returns (e.g., single VAT amount, breakdown, total with VAT) or how it handles ambiguous inputs like missing category. This is adequate for simple use but leaves gaps for an AI agent trying to predict exact output.

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 descriptions provide full coverage (100%) for all five parameters, so the description doesn't need to compensate. The description adds some context by mentioning 'category' and 'region' but doesn't elaborate on parameter interactions or constraints beyond what the schema already states. Baseline 3 is appropriate given the high schema coverage.

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 clearly states the tool's function with a specific verb ('Calculate') and resource ('Portuguese VAT'), and adds valuable scope modifiers (amount, category, region, and the special cases of Mainland/Azores/Madeira and intra-community B2B reverse charge). This makes it distinct from the unrelated sibling tools (e.g., categorise_expenses, draft_invoice).

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 description gives clear context for when to use the tool: for Portuguese VAT calculations with specific regions and B2B scenarios. It does not explicitly list exclusions or alternatives, but since none of the sibling tools perform VAT calculations, the intended use is evident. It falls short of a 5 because it doesn't explicitly state when not to use it or direct users to alternatives.

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