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

Annotations already cover safety (readOnly, idempotent, closed-world), so the bar is lower. The description still adds value by explaining the stacked-discount math (25% + 10% = 32.5%, not 35%), i.e. the second discount applies to the reduced price rather than the original.

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?

Front-loaded with the core output and the key stacking rule; the illustrative example earns its place. The trailing web-page URL is marginally useful and slightly dilutes the otherwise tight phrasing.

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?

With no output schema, the description does the work of naming the return values (sale price, savings, stacked total), which is sufficient for a simple, all-optional calculator. Nothing critical for invocation is missing.

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 all four parameters are already documented, including the 'extra' parameter's note that it applies to the already-reduced price. The description's stacking example reinforces this but adds no new parameter syntax or format detail beyond the schema.

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+resource: computes sale price, savings, and stacked-discount total for a percent-off. The stacking example is distinctive and would help an agent distinguish it from generic siblings like percentage_calculator, but no sibling is named explicitly.

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?

Usage is implied by 'for any percent off', but there is no explicit when-to-use, when-not-to-use, or routing to alternatives such as percentage_change_calculator or markup_calculator. Given the very large sibling set of calculators, this is a real gap.

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