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

Annotations already indicate this is a write operation (readOnlyHint=false) and non-destructive (destructiveHint=false), and the description's 'Creates a crypto invoice' is consistent with that. It adds audience context, but doesn't disclose side effects such as whether calling it generates a payable obligation, whether invoices expire, or whether payment must later be verified via the status tool.

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?

Three short sentences, each earning its place: the first states the action and audience, the second and third explicitly route non-target users to the correct alternatives. Information is front-loaded and there is 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?

The description is strong on purpose and routing, and an output schema exists to cover return values. However, it leaves the required packageId unexplained, which is a significant gap for a tool that cannot be invoked correctly without knowing what packageId should contain.

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 needed to compensate for the undocumented parameters. It only hints at 'web/Telegram' mapping roughly to the platform enum, but says nothing about the required packageId, returnUrl, or cancelUrl semantics. An agent would still need to guess what packageId refers to.

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 verb ('Creates'), a precise resource ('crypto invoice (NOWPayments)'), and the intended context ('human web/Telegram top-ups'). It also implicitly differentiates from siblings by naming what this tool is not for: ChatGPT humans and autonomous agents/bots.

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?

The description gives explicit when-to-use guidance for human web/Telegram top-ups and clearly names alternatives: ChatGPT humans should use https://ucode.uk/app/credits, and autonomous agents/bots must pay via USDC on Base through x402, not NOWPayments. This leaves no ambiguity about when to choose this tool.

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