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

No annotations exist, so the description carries the full burden. It discloses the checksum algorithm, date-of-birth and sex decoding on success, and the special invalid-date condition. However, it omits other behavioral aspects like what happens with incorrect length or non-digit inputs, or whether it checks real assignment.

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 relatively concise—one dense sentence covering purpose, algorithm, and outcomes. It could be improved by splitting into shorter sentences for readability, but it wastes no words and front-loads the core function.

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 it has only one parameter and an output schema (implied by mention of decoded data), the description covers validation logic, success behavior, and an edge case (invalid date). It is missing details on input length validation and what errors are returned for malformed inputs.

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 schema parameter description states 'digits-only identifier'. The tool description enriches this by specifying the context (Polish national ID), required length (11 digits), and the exact validation logic, adding significant 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 explicitly names the resource (PESEL) and action (validates checksum), specifies it's an 11-digit Polish national ID, and details the algorithm. This clearly distinguishes from siblings (nip_validate, regon_validate) by function and context.

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 use for PESEL numbers, but provides no explicit guidance on when to use this tool versus the sibling tools for NIP or REGON. No when-not conditions or alternatives are mentioned.

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