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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so the safe pure-calculation profile is covered. The description adds the useful behavioral fact that it handles combined state/county/city rates, but says nothing about output format, precision, or how the default region/currency interact with results.

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 plus an illustrative example and a URL — front-loaded and largely waste-free. The trailing web-page link is the only low-value element, but it does not impede comprehension.

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 zero-required-parameter, five-parameter pure calculator with full schema coverage and no output schema, the description conveys the core operation and its two directions. It is nearly complete; only the absence of sibling routing and result-format expectations keeps it from a 5.

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%, so mode, rate, amount, region and currency are all documented in the schema itself. The description's example ($127.50 at 6.25%) loosely illustrates the rate/amount relationship but adds no syntax or constraint detail beyond what the schema already provides. Baseline 3 applies.

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 and resource: 'Add sales tax to a price or pull it out of a receipt,' with a worked numeric example that makes the add/remove duality concrete. It does not explicitly differentiate itself from siblings like vat_calculator or gst_calculator, relying on the reader to know 'sales tax' is a distinct tax type.

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 example and the phrase 'combined state, county and city sales tax rate' imply when the tool applies, but there is no explicit when-to-use/when-not guidance and no routing away from the many tax-adjacent siblings (vat_calculator, gst_calculator, income_tax_calculator). Usage is inferable rather than stated.

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