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

With no annotations provided, the description carries the full burden. It discloses the main behavior (invoice creation), a key precondition (proof of npub ownership), and the follow-up action (call check_payment). It also clarifies cost ('Free — no credits required to call'), which is a useful behavioral caveat, though it omits details like invoice expiration or rate limits.

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 four concise sentences, front-loaded with the main purpose, followed by the usage flow and a free-to-call note. Every sentence earns its place with no redundancy 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?

Given the overall complexity, the schema richness (including output schema and detailed parameter descriptions), and the description's clear explanation of the invoice-payment-confirm flow, the tool definition is complete. The description covers the essential context: what it does, how to use it, prerequisites, and cost, without needing to explain return values because an output schema exists.

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 input schema has 100% coverage, including extremely detailed descriptions for all three parameters, especially the dpop_token format and requirements. The description adds only a general note about npub ownership but does not repeat or enhance parameter-level details; baseline 3 is appropriate when the schema does the heavy lifting.

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 opens with 'Buy credits via Bitcoin Lightning,' which clearly states the action (buy), the resource (credits), and the method (Lightning). It distinguishes this tool from siblings by describing the specific invoice-payment flow and next step (check_payment).

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?

Provides explicit steps: creates a Lightning invoice, pay it, then call check_payment to confirm. Also notes that proof of npub ownership is required and that the call is free, which helps the agent decide when to use it. However, it does not explicitly name alternative tools or when-not-to-use scenarios.

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