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

The description adds meaningful behavioral detail beyond the readOnlyHint annotation by specifying the validation methods (Luhn check, network detection). However, it doesn't specify the return value format (boolean vs. detailed object), which is a minor gap given no output schema is provided.

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 that conveys the core purpose and key behavioral details without any fluff. 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?

While the tool is simple with one parameter and clear annotations, the lack of an output schema and the ambiguity around 'network detection' (does it return a boolean, the network name, or a full validation report?) leaves the description slightly incomplete. A more explicit statement about the return value would make it fully complete.

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 already provides a clear description for the 'number' parameter ('Credit card number to validate'), achieving 100% coverage. The tool description adds context about what validation is performed but doesn't elaborate on parameter formatting or constraints beyond the schema.

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 validates a credit card number using specific algorithms (Luhn check, network detection). The verb 'validate' and resource 'credit card number' are precise, and it distinguishes itself from sibling tools like security_decrypt or lookup_breach_check by focusing exclusively on credit card validation.

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 context is clear: use this tool when you need to validate a credit card number. While it doesn't explicitly mention when not to use it or name alternatives, the unique purpose among siblings makes the usage unambiguous. There's no confusion with other tools.

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