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

With no annotations, the description carries the burden and does well: it discloses that this only creates an invoice (not a completed purchase), that payment happens externally in a Lightning wallet, that a separate check_payment call is needed, and that npub ownership proof is required. It omits invoice expiry, failure handling, or rate limits, keeping it below a 5.

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 lines, front-loaded with the core action, followed by the workflow and prerequisites. Every sentence earns its place and nothing is redundant.

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, and the description covers the essential multi-step workflow and auth prerequisite. Minor gaps around invoice lifetime and error behavior remain, but the agent has what it needs to invoke 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 description coverage is 100% and the dpop_token/amount_sats fields are documented in detail in the schema itself. The description adds no parameter-level detail beyond what the schema already provides, so the baseline 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 and resource ('Buy credits via Bitcoin Lightning') and immediately identifies the mechanism (Lightning invoice). It is clearly distinguishable from siblings like check_payment or check_balance, which it names as the follow-up step.

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?

Gives the full usage flow: create invoice, pay with any Lightning wallet, then call check_payment to confirm. Also states the npub-proof prerequisite and that the call is free. It lacks explicit when-not guidance or a named alternative for other purchase paths, so it stops short of a 5.

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