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

With no annotations, the description carries the behavioral burden. It discloses that the tool creates an invoice, requires proof of npub ownership, and is free to call. It does not mention invoice expiration or immediate ledger effects, but it explains enough about the flow and side effects for an agent to invoke it safely.

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 compact and front-loaded, with the main purpose in the first sentence, the execution flow in the next two, and a final cost-relevant detail. Every sentence earns its place, and there is no redundant phrasing.

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?

For a tool with three parameters, full schema coverage, and an output schema, the description provides enough context to call it correctly. It explains the required ownership proof, the payment workflow, and the follow-up confirmation step. Nothing essential is missing for agent selection and invocation.

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 description coverage is 100%, so the parameter burden is already met by the input schema. The description adds only a high-level mention of npub ownership, which maps to the dpop_token parameter. This is sufficient but does not go beyond the schema in meaningful ways.

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 a specific verb and resource: 'Buy credits via Bitcoin Lightning.' It further clarifies the mechanism by saying it creates a Lightning invoice, so an agent immediately knows this is the tool for purchasing credits, not for checking payment status or redeeming coupons.

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 gives clear operational guidance: pay with any Lightning wallet, then call check_payment to confirm. It also states the prerequisite of proving npub ownership. It doesn't explicitly discuss alternatives, but the tool is the obvious entry point for buying credits and mentions the follow-up tool, so the context is clear.

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