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

With no annotations, the description carries the burden of explaining behavior. It usefully describes the digit-square repetition and stopping condition, but it does not specify the return value, input mechanism, or side-effect profile unambiguously.

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 compact and front-loaded with the core purpose, and the algorithm detail is useful. The redundant 'Is Happy:' prefix and the vague 'Provide value' tail keep it from being excellent.

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?

No output schema or annotations exist, and the empty input schema conflicts with the need to provide a numeric value. The description explains the predicate concept but leaves the invocation contract incomplete for an agent.

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?

The schema has zero properties yet the description instructs to 'Provide value,' naming no parameter, type, or format. This creates an unresolved conflict between the expected input and the declared schema, making invocation ambiguous.

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 clearly states a specific action (check whether a number is happy) and defines the algorithm. However, it does not distinguish this tool from the near-identical sibling x402-is-happy-number, so it lacks explicit differentiation.

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?

No guidance is given about when to use this tool instead of related predicates like x402-is-happy-number or other is-number tests. An agent must infer the intended scope from the name alone.

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