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

With no annotations provided, the description carries the full behavioral burden. It discloses that this call only creates an invoice, that external payment is required, that confirmation happens via check_payment, and that proof of ownership is needed. It stops short of mentioning invoice expiry or ledger-side effects, but the essential behavioral traits are visible.

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 short, front-loaded, and every sentence earns its place: what the tool does, how the payment flow works, the ownership prerequisite, and the free-call caveat. It is easy to scan and contains no 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 output schema and full parameter documentation, the description provides enough contextual guidance for correct invocation: it covers the purchase flow, the required proof of ownership, and the needed follow-up call. Minor details such as invoice expiry or amount limits are absent, but they are not essential for selecting and invoking the tool correctly.

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%, and the schema already documents npub, dpop_token, and amount_sats thoroughly. The description adds useful context about why ownership proof matters, but it does not meaningfully expand parameter meaning beyond the structured schema, so the baseline score of 3 is appropriate.

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 clearly explains the invoice workflow and names the follow-up tool check_payment, so an agent can distinguish this from the many sibling tools such as check_balance or restore_credits.

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 a clear usage flow: create the invoice, pay it with a Lightning wallet, then call check_payment to confirm. It also states a key prerequisite — proof of npub ownership — and that the call itself is free. It does not explicitly enumerate when not to use the tool or compare it to alternatives, but the workflow guidance is strong.

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