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

No annotations exist, and the description does not add behavioral context beyond the basic check. It does not mention that the tool is read-only, has no side effects, or that it only works for non-negative integers (though implied by schema). For a simple tool this might suffice, but more transparency is expected without annotations.

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, efficient sentence. However, it could be slightly improved by explicitly stating the return value (e.g., 'Returns true if the number is an Armstrong number, false otherwise'). Still, it is concise and front-loaded.

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 simple boolean check with one parameter and an output schema (likely boolean), the description is adequate but lacks definition. A brief explanation of Armstrong number (e.g., 'a number that is equal to the sum of its own digits each raised to the power of the number of digits') would improve completeness for non-expert users.

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 parameter schema has 100% coverage with a description 'Number to check'. The tool description adds no extra semantic detail beyond that. It does not explain what an Armstrong number is or how it's computed, which could be useful but is not strictly necessary given the name. Baseline 3 is appropriate since schema does the heavy lifting.

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?

Clearly states the tool checks if a number is an Armstrong number (narcissistic number). The verb 'check if' and resource 'a number' are specific. Distinguishes from sibling tools like is_prime or is_perfect_number by naming the exact property.

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?

Provides no guidance on when to use this tool versus alternatives. With many sibling number property checkers (is_prime, is_perfect_square, etc.), some explicit when-to-use or when-not-to-use advice would be beneficial.

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