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

No annotations are provided, so the description carries the full burden; "Pure CPU, instant" usefully discloses that this is a cheap, side-effect-free, non-networked computation. However, it is silent on what happens when the optional percent parameter is omitted, and does not state whether results are rounded or how precision is handled — meaningful gaps for a numeric tool.

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?

Two short sentences, zero filler, and the capability with its return values is front-loaded before the performance note. Every clause earns its place.

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 trivial two-parameter pure function with no output schema, the description is nearly sufficient — it names the operation and enumerates the three return values, which substitutes for the missing output schema. The only real omission is the behavior of the non-required percent parameter.

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% with both parameters documented ("Original price", "Discount percent"), so the schema already does the heavy lifting and the baseline applies. The description adds no interpretation of units (is percent 0-100 or 0-1?) or the optional-parameter default, which is exactly the kind of meaning the schema leaves out.

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?

"Apply a percentage discount to a price and return the sale price, amount saved and effective rate" gives a specific verb (apply), resource (percentage discount on a price), and even the return fields. It does not name a distinguishing boundary against nearby siblings like percentage_calculator or tip_calculator, so it stops short of a 5.

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 phrase "apply a percentage discount to a price" implies the usage context (markdown/sale-price math), but there is no explicit when-to-use guidance and no routing to alternatives such as percentage_calculator or tip_calculator, which occupy adjacent territory in the sibling list.

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