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

No annotations are provided, so the description must convey behavior. It states the tool creates a Lightning invoice, requires proof of npub, and that calling it is free. This provides sufficient transparency for the agent to understand side effects.

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 three sentences long, front-loaded with the core purpose, and every sentence provides essential information (invoice creation, payment process, proof requirement, free usage). No wasted words.

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 description doesn't need to explain return values. It covers the purchase flow, prerequisites (dpop_token), and post-call step (check_payment). This is complete for a payment creation tool.

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%, but the description adds critical details for the dpop_token parameter: it must be raw JSON of a kind-27235 Nostr event with specific formatting constraints, which is far more helpful than the schema alone.

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 starts with 'Buy credits via Bitcoin Lightning', which clearly states the action and resource. It distinguishes itself from siblings like weather_check_balance and weather_check_payment by focusing on purchasing.

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?

The description explains the flow: create invoice, pay, then call check_payment. It also notes the requirement of npub ownership proof. While it doesn't explicitly list when not to use, the context is clear for a purchase tool.

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