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

Despite readOnlyHint=true and openWorldHint=true annotations, the description adds substantial behavioral context: response shape depends on 'kind', URL expiry and refresh, 'source' semantics, and untrusted note field. It also explains error states and verification timing, which annotations alone would not convey.

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 dense but every sentence contributes essential information. It front-loads the core purpose, then systematically covers conditional response fields and error handling. The structure is logical and avoids redundancy, earning its length.

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 fully documents the response structure (kind, url, expires_at, content_type, bytes, sha256, source, note) and error semantics. It covers authentication, authorization, event timing, and retry behavior—everything an agent needs to call it correctly.

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 single parameter 'purchase_id' is not described in the schema (0% coverage), but the description's context makes its purpose clear. It doesn't elaborate on format or source, but given the name and usage context, an agent can infer it. The description adds enough implicit meaning to compensate for the schema gap.

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 states a specific verb ('Fetch') and resource ('what was delivered against a purchase'), clearly distinguishing this from sibling tools like getListing or myPurchases. It also clarifies scope (buyer/seller only), making the purpose unambiguous.

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 provides usage conditions: requires API key, only buyer or seller, and explains when to poll versus wait for the 'delivery.sent' event. It also clarifies the 'not_found' error is non-retryable until delivery occurs, giving clear guidance on when not to use the tool.

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