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

Annotations already indicate readOnlyHint=true, confirming no destructive behavior. Description adds that validation is structural only, clarifying it does not check against external databases. No contradictions.

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?

Two sentences with zero redundancy. All information is front-loaded and directly relevant to usage, behavior, and scope.

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 validation tool with one parameter and no output schema, the description explains what is validated (format and check digit) and what is not (structure only). Lacks explicit return value description, but the purpose is clear.

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 provides 100% coverage with a clear description for the single parameter (curp: 'The 18-character CURP (case-insensitive).'). The description's note about not guessing check digits is useful context but does not add new parameter meaning 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 Mexican CURP format and check digit, specifying the exact resource (Mexican CURP) and action (validate structure). It is distinct from sibling validation tools targeting different identifiers.

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?

Explicitly instructs when to use ('USE THIS to verify a Mexican CURP before relying on it') and warns against guessing check digits. Does not explicitly mention alternative tools, but given the specific identifier, no direct alternative exists.

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