is_prime

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

With no annotations, the description carries the behavioral burden, and it does establish that the tool is a pure predicate returning a yes/no answer. It does not disclose edge-case behavior for 0, 1, negative integers, or very large numbers, which are all accepted by the schema as integers.

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 a single, front-loaded sentence with no filler. Every word 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 single-parameter pure predicate with an output schema available, the description covers the essential behavior. It is slightly incomplete only in its silence about non-standard inputs like 0, 1, and negative numbers.

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%, so the description needed to compensate by explaining the parameter's meaning and constraints. It only says 'a number,' which is nearly the same as the parameter name and type, and does not clarify that the input should typically be a positive integer greater than 1 or how edge cases are handled.

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?

The description uses a specific verb ('Return whether') and a clear resource ('a number is prime'), making the tool's predicate behavior immediately obvious. It is easy to distinguish from the listed arithmetic siblings, since none of them test primality.

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 rather than explicitly stated: if an agent needs to know whether a number is prime, this is the tool to call. However, the description does not explicitly discuss when not to use it or mention alternatives, though the sibling tools are all clearly different operations.

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