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

Annotations declare readOnlyHint, idempotentHint, and closed-world, but the description adds significant behavioral detail: pricing ($0.001 per check paid via x402 in USDC on Base), that the input is never echoed or stored, and that personal identifiers are masked. This goes well beyond the annotations and helps the agent understand cost, privacy, and output behavior.

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 tight sentence that front-loads the validation rule, then covers cost, payment mechanism, return shape, and privacy. Every clause earns its place with no redundancy.

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 single-parameter validation tool with no output schema, the description tells the agent what is validated, how much it costs, how payment works, what the return shape is, and privacy guarantees. No output schema exists, so explaining the return value is beneficial and included.

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 coverage is 100% and the single parameter is fully described in the schema (with example). The description does not add syntax or format details beyond what the schema provides. Baseline 3 is appropriate.

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 states a specific verb (validate) and resource (Polish NIP tax id) and gives the exact validation method (10 digits + weighted mod-11 checksum). It is clearly distinguishable from siblings like validate_pl_pesel and validate_pl_regon by naming the specific identifier.

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 implies the tool is for checking Polish NIP tax IDs but provides no explicit guidance on when to use it versus alternatives such as validate_pl_pesel or validate_eu_vat. There are no exclusions or conditions for selecting this tool over siblings.

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