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

With no annotations, the description carries the behavioral burden and does disclose meaningful traits: the operation is free, and it requires proof of npub ownership with the stated security rationale (preventing credit-grant front-running). It does not state read-only/idempotency or failure behavior, but return shape is covered by the output schema.

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?

Four short fragments, front-loaded with the core action, then sequencing, cost, and auth rationale. Every sentence carries information with no filler, though it is slightly terse rather than richly structured.

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. The description covers purpose, when to call it, cost, and auth requirements, which is sufficient for an agent to invoke it correctly. Minor gaps (read-only nature, error handling) are not critical here.

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 schema already fully documents all three parameters (npub, dpop_token, invoice_id). The description adds no parameter syntax or format detail beyond the schema, so the baseline of 3 applies.

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?

States a specific verb+resource: 'Check the payment status of a Lightning invoice.' The resource is distinct from the many sibling check_* tools (check_balance, check_price, check_proof_status). It does not explicitly name a sibling it is not, so it falls short of a 5, but the resource is unambiguous.

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?

'Call after paying the invoice from purchase_credits' gives clear sequencing context and ties it to a named sibling tool. It also notes the cost model ('Free — no credits required'). It lacks explicit when-not-use or alternative-tool guidance, so not a 5.

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