is_nan

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states what the tool does but doesn't describe how it behaves: e.g., whether it handles non-numeric inputs gracefully, returns a boolean, or throws errors. For a simple comparison tool, this is a moderate gap, as the agent lacks operational details beyond the basic check.

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 extremely concise and front-loaded: a single sentence stating the tool's purpose, followed by a brief parenthetical for context. Every word earns its place with no redundancy or fluff, making it easy for an agent to parse quickly.

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?

Given the tool's low complexity (one parameter, simple boolean output), no annotations, no output schema, and 0% schema description coverage, the description is minimally adequate. It states the core purpose but lacks details on behavior, error handling, or output format. For such a simple tool, this is borderline acceptable but leaves gaps an agent might need to infer.

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 input schema has 1 parameter (x) with 0% description coverage, so the schema only indicates it's a number. The description doesn't add any parameter semantics beyond implying 'x' is the number to check. This meets the baseline of 3 since the schema provides the type, but the description doesn't compensate for the lack of schema descriptions (e.g., explaining NaN semantics for 'x').

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 the tool's purpose: 'Check if a number is NaN (Not a Number).' It includes a specific verb ('Check') and resource ('a number'), and the parenthetical adds domain/category context. However, it doesn't explicitly distinguish this from sibling tools like 'is_finite' or 'is_infinite' that also check number properties, though the NaN focus is inherently distinct.

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 description provides no guidance on when to use this tool versus alternatives. It mentions the domain ('arithmetic') and category ('comparison'), but doesn't specify scenarios (e.g., validating input after division by zero) or contrast it with similar sibling tools like 'is_finite' or 'is_infinite'. Without such context, an agent must infer usage 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.