Buy a trial prepaid capacity pass — $0.50 for 20 calls, 7 days (PAID $0.50)

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

Annotations already declare readOnly=false, openWorld=true, idempotent=false, destructive=false, so the safety bar is lower. The description adds genuinely useful context the annotations don't carry: it is a paid operation costing 0.50 USD in USDC on eip155:8453 via x402, and it hits POST /v1/pass/purchase/trial, which tells the agent a real charge occurs. It does not state what happens on repeat calls (whether passes stack) or what expires after the 7 days.

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 short lines, front-loaded with price and quantity, which is good. However, the first sentence restates the title almost verbatim, spending words on information the agent already has in the title field rather than on new guidance.

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?

An output schema exists, so return values need not be explained, and with zero parameters the surface is small. Still missing for a paid, non-idempotent purchase: whether the 7-day window starts at purchase, whether buying again extends or duplicates capacity, and how the x402 payment is actually settled by the agent.

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 tool takes zero parameters, so the schema leaves nothing ambiguous and the baseline is 4. The description correctly introduces no parameter concepts, implying the purchase is fully determined by the caller's identity.

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?

Specific verb+resource with concrete terms: buy a trial prepaid capacity pass, 20 calls, 7 days, $0.50. The 'trial' qualifier implicitly separates it from the sibling v1_pass_purchase, but the description never names that sibling or states the contrast explicitly.

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?

There is no statement of when to choose this over v1_pass_purchase, no prerequisite or eligibility note, and no guidance on whether a trial can be bought repeatedly. The only hint is the word 'trial' in the name and title, which the agent must infer from.

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