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

With no annotations, the description carries full burden. It discloses the operation (accepts payment), the credit source, and return format (json with 'values'). But it does not mention potential side effects (balance deduction, invoice status change), failure modes (insufficient credit), or reversibility. This adds some context but remains incomplete.

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 three sentences, front-loaded with the primary action, followed by useful context and clear parameter annotations. No redundant words or filler—every sentence adds value.

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 two-parameter payment tool, this description covers the core aspects: operation, credit source, invoice origin, and return envelope. The output schema exists, so detailed return fields are not necessary. Missing preconditions and failure behavior, but overall adequate for the tool's complexity.

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 provides explicit @param docs for both parameters, identifying them as database IDs and tying invoice_id to customer_log_subscription. This gives useful meaning beyond the schema's bare integer types, though customer_id lacks detail on how to obtain it.

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: 'Accepts a subscription payment from the customers prepaid credit.' It clearly identifies the resource (subscription payment via prepaid credit) and differentiates from siblings like paywall__pay_subscription_with_wallet and paywall__pay_subscription_with_ott_voucher by specifying the credit source. It also links the invoice to customer_log_subscription.

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?

Provides clear context on when to use the tool: when paying with prepaid credits, and explains how credits arrive (over-payment or netfluid_wallet_transfer). It also states invoice_id originates from customer_log_subscription. However, it does not explicitly exclude alternatives or state when not to use it, so it misses the full 'when-not' guidance.

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