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

With no annotations, the description carries the full burden and does well: it discloses that real webhooks fire, that test keys are required, and the state transitions tied to confirmations. It stops short of covering irreversibility, rate limits, or the effect of delay_seconds/from_address.

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?

Four compact, front-loaded sentences with no filler; the key constraint (test keys only) and the state-transition mappings are stated in shorthand that an agent can act on immediately.

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 7-parameter, no-output-schema mutation tool, the description covers the essential mechanics (state machine, webhooks, confirmations thresholds, tx_hash reuse). The two underexplained parameters and absence of error/response behavior leave a minor gap.

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?

Only confirmations, tx_hash, and amount get meaningful semantic treatment (advance same payment, underpaid/overpaid). At 57% schema coverage, from_address and delay_seconds are undocumented in both places, so the description only partially compensates.

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 ('Create a synthetic on-chain payment') scoped to invoice (inv_) or credit purchase (cpu_) IDs, and clarifies it drives the real state machine and webhook pipeline. This clearly separates it from siblings like create_credit_purchase or list_payments.

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?

Explicitly restricts usage to test keys and explains the confirmations-based outcomes plus how to simulate underpaid/overpaid. It gives strong operating context, but never names an alternative tool or an explicit 'do not use in production' exclusion beyond 'test keys only'.

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