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

With no annotations provided, the description carries the burden and does well: it discloses that the call is free, requires proof of npub ownership, and explains the security rationale about preventing credit-grant front-running. It does not detail failure modes or explicitly state read-only behavior, but the purpose verb 'check' and the explanation provide solid transparency.

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 sentences, each earning its place: purpose, call timing, cost, and auth rationale. The most important operational guidance is front-loaded, and there is no filler or repetition of schema content.

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 a rich input schema and an output schema, the description supplies the missing operational context: when to call, that it is free, and why the dpop_token proof is required. An agent has everything needed to select and invoke this 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 description coverage is 100%, so the schema already documents all three parameters thoroughly, including the exact source of invoice_id and the raw JSON form of dpop_token. The tool description adds workflow context but no new parameter-level meaning beyond the schema. Baseline 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?

States a specific verb and resource: 'Check the payment status of a Lightning invoice.' This clearly differentiates it from sibling check tools like check_balance, check_price, and check_proof_status. It also anchors the workflow by referencing purchase_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?

Explicitly says when to call: 'Call after paying the invoice from purchase_credits.' It also gives cost context ('Free — no credits required') and an auth requirement, though it does not name alternative tools or exclusions. This is clear usage guidance without needing to reference siblings.

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