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

Annotations already declare this as read-only and non-destructive. The description adds behavioral detail beyond annotations: it automatically detects Master Numbers, reduces double-digit days, and returns 300-500 word interpretations with specific thematic content. This gives an agent useful expectations about the computation and output.

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 front-loaded with the core action and meaning, and the later sentences provide behavioral and use-case context. It is somewhat longer than strictly necessary, with promotional phrases like 'Perfect for talent discovery apps', but every section serves some purpose.

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?

With three parameters, no output schema, and no nested objects, the description covers the main behavior, Master Number handling, output length, and use-case domain. It does not fully define the exact response structure, but the description is complete enough for an agent to decide when and how to call the tool.

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 100%, so the input schema already documents all parameters, including day constraints, lang enum, and compact behavior. The description adds minor conceptual context about the day parameter but does not meaningfully extend the schema's parameter semantics.

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 first sentence clearly states the verb ('Calculate'), the resource ('Birth Day number'), and the input ('day you were born 1-31'). It also describes the meaning ('special talents and abilities'), so an agent can identify the tool's unique purpose. However, it does not explicitly contrast itself with sibling tools like life_path or expression.

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 clear use-case guidance through 'Perfect for talent discovery apps, career counseling platforms, personal development services, and skill assessment tools.' It implies when to use this tool but does not explicitly state when not to use it or name alternatives, so it falls short of a full exclusion-based recommendation.

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