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

With no annotations provided, the description carries the full behavioral burden and mostly delivers: it explains that mode='add' treats the amount as GST-exclusive while 'remove' treats it as GST-inclusive, and adds rate context (historical 0.125, 0.10 for Australia). It does not disclose rounding behavior or the exact output shape, which is a modest 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?

Purpose is front-loaded in the first sentence, followed by usage scope, examples, and dense parameter documentation in a logical order. The 'Common use cases' list partially overlaps with the earlier use-case enumeration, so it is slightly redundant, but every section serves a purpose and nothing 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?

For a 3-parameter calculator with no annotations and no output schema, inputs and intended uses are well covered, but the description never states what the tool returns. The examples ('how much GST is in a $230 total' vs 'remove GST from $1,150') leave ambiguity about whether the result is the GST amount, the adjusted total, or both, and rounding rules are unspecified.

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 0%, and the description fully compensates: amount is clarified as 'Dollar amount in NZD,' mode's enum values get operational meaning ('treats amount as GST-exclusive... GST-inclusive'), and gst_rate receives default, historical, and cross-country context. Every parameter gains meaning well beyond the bare schema titles.

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?

Opens with a specific verb+resource statement — 'Add or remove New Zealand GST (15%) from a dollar amount' — and reinforces it with concrete examples ('what's $500 plus GST', 'how much GST is in a $230 total'). The GST domain is unique among the 29 sibling calculators, so an agent can distinguish it without opening the 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?

Provides explicit when-to-use guidance: 'Use this tool for ANY question about NZ GST: adding GST to a pre-tax price, extracting GST content from a GST-inclusive total, reverse-calculating GST, or checking GST on invoices and quotes.' It does not name explicit when-not-to-use exclusions, though sibling calculators occupy clearly different domains, making the routing unambiguous.

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