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

Annotations already declare readOnlyHint=true and openWorldHint=false; the description reinforces the offline nature and adds substantive detail about what the check actually computes (Luhn check digit with prefix 80840) plus a clear negative capability statement. It stops short of describing the response shape or how failures are reported per item.

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, zero filler, with the core operation stated first and the limitation/alternative second. Every clause earns its place.

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 validator with no output schema, the description covers what is validated, the input constraints, and the scope boundary against lookup_npi. The only gap is how per-item results or invalid inputs are returned, which the agent must discover by calling.

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 0%, so the description must carry the burden, and it does: it defines the expected format (10 digits, Luhn-valid, prefix 80840) and the batch limit of 50, which the schema only encodes as maxItems without explaining the underlying constraint. It does not clarify error behavior for malformed entries.

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 verb and resource ('Offline check of ... NPI numbers') and specifies exactly what is checked: 10 digits, Luhn check digit, prefix 80840. This is clearly distinguishable from lookup_npi, which it names.

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 states the limitation ('Does not call CMS, so it cannot say whether the number is issued') and routes the agent to the correct alternative ('use lookup_npi for that'). When-to-use and when-not-to-use are both covered.

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