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

Annotations already flag destructiveHint=true and openWorldHint=false, so the description's real contribution is the billing model: one people credit per matched person, one property credit per included property, and no charge on a miss. That cost/auth detail is exactly the kind of behavior an agent needs before spending credits. It does not explain why the call is flagged destructive or how multiple matches are resolved.

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 with the core action first, then the return shape, then billing. Nothing is padding, though the semicolon-chained billing clause is dense and could be split for scanability.

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?

With no output schema, the description correctly takes on the job of listing returned fields (name, contact info, demographics, optional properties). Auth and cost are covered, but ambiguity around multiple phone matches and the effect of the location parameter is left unresolved.

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%, so phone formatting, the fields array, and the location object are already documented. The description only restates the include_properties cost and the required phone, which the schema already carries, and says nothing about how location narrows matches. 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?

States a specific verb and resource plus the identifier ('Looks up a person by phone number'), which cleanly separates it from enrich_name, enrich_email, enrich_address and enrich_apn. It also enumerates what comes back, so the agent knows the output shape before calling.

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 context is implied through the paid-account prerequisite and the credit model, which tells the agent this is a metered enrichment call. However, it never names an alternative (e.g., people_search or enrich_name) or states when not to use this tool, so no explicit routing guidance exists.

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