validate_card

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

With no annotations, the description fully discloses behavioral traits: it performs Luhn checksum, brand detection, and length verification, but explicitly states it does not check card existence, activity, or funds. 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?

Description is two sentences: the first commands usage and sets context, the second specifies what it does and does not. Extremely concise and front-loaded with no redundant information.

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 no output schema and one parameter with full schema coverage, the description is remarkably complete. It covers purpose, actions, exclusions, and parameter behavior adequately for an AI agent.

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 covers the single parameter 'number' at 100% with description of ignoring spaces/dashes. The description adds value by explaining the validation operations performed on that number, which goes beyond the schema's parameter description.

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 it validates a payment card number's structure, Luhn checksum, brand detection, and length. It distinguishes from siblings like validate_iban, validate_isbn, and validate_vin by targeting payment cards specifically.

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 to use this tool before using a card number, advises against assuming validity or guessing brand, and clarifies what it does NOT check (real, active, funds). However, it does not mention when to use alternatives or when not to use this tool.

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