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

With no annotations, the description carries the full burden. It discloses that the tool creates an invoice (not immediate credit), requires proof of npub ownership, and is free. It also indicates that payment is confirmed via check_payment, which is important behavioral context not in the 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?

The description is compact and front-loaded: first sentence states the purpose, followed by a concise workflow and cost note. Every sentence adds value with no redundancy.

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?

The description covers the entire flow: creates invoice, payment via any wallet, follow-up with check_payment, and the auth requirement. It also notes the cost. Output schema exists, so return details are not needed. Given the tool's simplicity, this is complete.

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 parameter descriptions are already detailed. The tool description reinforces that dpop_token is proof of ownership but does not add syntax or format details 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?

The description states 'Buy credits via Bitcoin Lightning' with a specific verb and resource. It clearly distinguishes from siblings by explaining it creates a Lightning invoice and leads to a check_payment workflow, unlike balance checks or other tools.

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?

It gives clear context on when to use: to purchase credits, and it names check_payment as the next step, implying a workflow. It also notes 'Free — no credits required to call,' which clarifies a prerequisite. However, it does not explicitly mention alternatives or when not to use.

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