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

Annotations only declare readOnlyHint and openWorldHint; the description adds materially important behavior an agent cannot get from structured fields: a per-call cost ($0.002 USDC), the x402 payment requirement and chains (Base, Solana, Arc), and that failed calls are free. That is exactly the kind of cost/authorization context an agent needs before invoking.

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?

Purpose is front-loaded in the first clause and the pricing/payment caveat sits at the end where it belongs. The long enumeration of returned fields consumes a lot of text and duplicates what the output schema already declares, which is the only real waste.

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 an output schema present, the return-field list is redundant rather than necessary, and the description correctly focuses on scope, input modes, and the paid-call model. What remains missing is any routing signal versus sibling pharmacy/price tools, though nothing prevents a correct invocation.

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 description coverage is 100%, so each parameter is already documented, and the description largely restates it ('search by drug name (optionally strength) or NDC'). The one extra nuance — the term-or-ndc mutual requirement — is also present in the schema, so 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 verb and resource: searches Cost Plus Drugs mail-order cash prices from its official pricing API, by drug name (+ optional strength) or NDC. It also scopes the data ('Only drugs sold on the CPD mail-order channel'), which distinguishes it from general pharmacy/retail siblings like ecommerce_singlecare or ecommerce_chewy_com.

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 by the search-mode enumeration ('search by drug name (optionally strength) or NDC') and by the constraint that either term or ndc is required. However, it never says when to prefer this over a sibling pharmacy-price tool (e.g. ecommerce_singlecare) or when-not to use it beyond the mail-order-channel limitation.

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