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

Annotations only cover the safety profile (readOnly, idempotent, closed-world). The description goes well beyond them by disclosing the paid access model ($0.001 per check via x402 in USDC on Base), the concrete return shape, and privacy behavior (input never echoed or stored, identifiers masked). These are exactly the operational facts an agent needs before invoking a metered tool.

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 tight sentences, front-loaded with purpose, then cost/payment, then return shape and privacy. Every clause carries distinct, actionable information 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?

No output schema exists, and the description compensates by naming the returned fields ({type, valid, normalized, reason}); it also covers cost, payment rail, and data-handling guarantees. For a single-parameter validator, nothing material is missing.

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% for the single 'value' parameter, so the schema already documents the input and gives an example. The description adds only tangential information (that the value is not echoed or stored), so the baseline 3 applies.

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?

States a specific resource (Polish PESEL) plus exactly what it verifies (checksum, encoded birth date and sex), which an agent can immediately distinguish from validate_pl_nip, validate_pl_regon, or validate_iban. The verb 'checks' is present in substance and the resource is unambiguous.

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?

Usage is implied: use this to validate/parse a Polish PESEL rather than any other identifier type, and the sibling names make the selection fairly obvious. However, the description never explicitly states when to prefer this tool, nor does it give prerequisites or exclusions relative to the other validators.

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