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

With readOnlyHint, openWorldHint, and idempotentHint annotations covering safety, the description adds useful context: prerequisite of payment, return of a verified download URL, and supported product slugs. It does not mention edge cases like URL expiration, but only a minor gap.

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?

Three sentences, each adding distinct value: action and prerequisite, authentication methods, and return type/product support. No redundant wording or filler.

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?

The description covers the core prerequisites (paid, product slug, auth identifiers), return value (verified download URL), and supported products. With no output schema, the only missing piece is explicit error/edge-case behavior, but the description is largely complete for its straightforward purpose.

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 descriptions already cover all three parameters (100% coverage). The description adds meaning by explaining the source and preferred flow for each identifier ('On-chain txHash from pay_merchant (preferred for agent flows)', 'Coal checkout sessionId'), and lists the exact product slug with price.

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 action ('Retrieve / download / get the file') for a clear resource ('digital product after the user paid for it'). It distinguishes itself from siblings like pay_merchant by requiring prior payment and from check_paywall by returning a download URL.

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 instructs to use 'after pay_merchant succeeds' for digital goods, and provides two authentication identifiers (txHash from pay_merchant, sessionId from Coal checkout) with preferences. This clearly defines when to use the tool versus alternatives.

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