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

With no annotations, the description must carry the behavioral burden, and it does disclose a non-obvious two-phase payment handshake and the accepted payment rails (x402, MPP, card link). It omits other important traits: whether the operation is idempotent, what happens on payment failure, whether credit is refundable, or minimum/maximum amounts.

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?

Two tight sentences with zero filler, and the core action is front-loaded before the payment-flow detail. Every clause carries operational information.

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 single-parameter tool this covers the action and the unusual payment flow, which is the main thing an agent needs. But it instructs the caller to 'call it again with the payment' while the schema exposes only 'amount', leaving a real ambiguity about how payment is actually conveyed.

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?

There is a single parameter with 100% schema description coverage, so the baseline is 3. The description adds no meaning beyond the schema (no constraints, bounds, or format guidance for 'amount'), and indeed introduces a payment concept the schema does not model.

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 ('Adds credit to your account'), which is clear enough to distinguish it from the read-only sibling 'balance'. It never explicitly names the sibling it complements, so differentiation is inferred rather than stated.

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 outlines a two-step protocol—call without payment to learn how to pay, then call again with payment—which is useful implied usage guidance. However, it gives no guidance on prerequisites (e.g., checking 'balance' first), no when-not-to-use conditions, and is ambiguous about how the payment is supplied given the schema exposes only 'amount'.

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