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

Annotations already declare the operation read-only, idempotent, and non-destructive. The description adds useful behavioral context beyond that: it is 'Keyless CMS data' and it specifies the output fields returned. It does not cover rate limits or error behavior, but for a simple lookup this is a strong disclosure.

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 tightly written sentences front-load the action and resource, then list the return fields and the keyless aspect. Every sentence earns its place with no filler or repetition.

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, read-only lookup with no output schema, the description is complete: it states the input requirement, the scope, the returned data, and the authentication context. Nothing essential 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?

The schema already fully describes the only parameter, 'npi', as a 10-digit NPI number, so parameter semantics are covered. The description reinforces the 10-digit requirement but adds no new 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 uses a specific verb ('Look up'), a specific resource ('single US healthcare provider'), and a precise identifier ('10-digit NPI'). It also enumerates the returned fields, making the tool's purpose immediately distinguishable from the many search siblings like npi_search_provider or npi_search_specialty.

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 clearly implies this tool is for looking up one provider when the NPI is already known, rather than searching by name or specialty. However, it does not explicitly name sibling alternatives or state when to use them instead, so it stops short of full routing guidance.

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