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

Goes well beyond the annotations by disclosing the asynchronous credit flow (balance credited only after on-chain confirmation), the single-unpaid-invoice invariant, the auth requirement, and the human-in-the-loop crypto payment step. These are exactly the behavioral traits an agent could not infer from readOnlyHint=false / idempotentHint=false alone.

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?

Front-loaded with purpose and return value, and generally tight. The automatic-credit behavior is stated twice (once mid-description, once in the final sentence), which is mild redundancy but not harmful.

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?

With no output schema, the description correctly supplies the return value (`checkout_url`) and explains what happens after the call. Required token, amount semantics, and the async confirmation path are all covered.

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 coverage is 100% and already documents the 3–10000 range, but the description adds that the amount is in account currency (USD) and that bounds are enforced server-side, clarifying failure modes not stated in the schema.

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+resource (create a top-up invoice) and the concrete artifact returned (`checkout_url`), which cleanly separates it from read-only siblings like get_balance and from pay_invoice. An agent knows immediately what this does and what it produces.

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 clear preconditions and constraints: amount in account currency, server-side min/max, one unpaid top-up at a time, requires token, and a human must complete payment. It doesn't name sibling alternatives (e.g., pay_invoice vs. this), so routing guidance is implied rather than explicit.

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