calculate_vat_breakdown

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

Annotations already declare readOnlyHint and idempotentHint, so the tool's safety is clear. The description adds behavioral context by detailing the output structure (lines_summary, vat_breakdown, totals) and input requirements, which goes beyond the annotations.

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 two sentences, each informative and front-loaded. The first sentence explains the function and output, the second gives use cases. No unnecessary 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?

Given the existence of an output schema, moderate complexity, and full parameter description coverage, the description is complete. It covers what the tool does, its inputs, outputs, and appropriate usage scenarios.

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 description adds little new information about parameters beyond what the schema already provides. It restates the required fields for line items but does not enhance understanding of the parameters.

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?

Description starts with a specific verb 'Calculates' and resource 'VAT breakdown', and explicitly states the scope 'for a list of invoice line items'. It clearly distinguishes itself from sibling tools like calculate_vat_amount by focusing on a complete breakdown with grouping.

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 provides explicit usage contexts: 'Use when generating invoices, building checkout summaries, or verifying VAT calculations'. It does not mention when not to use or alternatives, but the context is sufficiently clear.

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