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

With no annotations, the description must carry the behavioral burden. It discloses that this is a creation operation and what it returns, and it adds the 'min 100' constraint. However, it does not say whether the invoice expires, whether credits are credited automatically after payment, or any other side effects.

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 a single sentence that front-loads the core action, includes the key constraint, and lists the returned fields. Every phrase earns its place with 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?

For a simple one-parameter tool with no output schema, the description covers the action, the parameter constraint, and the return values. It is slightly incomplete because it does not connect this order to the surrounding sibling workflow, such as how the returned order_id is used after payment.

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 0%, so the description must compensate. It does by stating that credits are for 'STYX credits' and imposing the meaningful minimum of 100. The single parameter's purpose is reasonably inferable, though the description stops short of explaining how credits convert to an invoice amount.

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 a specific action and resource: 'Create a BTCPay invoice for STYX credits.' It also tells the agent what the tool returns ('order_id + checkout_link'), making it clearly distinct from any balance-checking, renewal, or key-collection sibling.

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?

There is no explicit guidance about when to use this tool versus alternatives like styx_credits or styx_renew. The intent to create a payment invoice is implied, but the description does not state exclusions, prerequisites, or workflow context.

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