Create a payment

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

With no annotations, the description carries the full burden and mostly succeeds: it discloses the sandbox default (testnet coins, nothing real moves), the idempotent external_id behavior, and the returned fields/status. It omits auth/credential requirements and any rate-limit or error behavior, which leaves a real gap for a write 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?

Front-loaded with the core action and the return value, and every sentence carries information (sandbox default, idempotency). It is slightly dense but there is no filler; the only mild redundancy is restating the sandbox notion across two clauses.

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 an 8-param write tool with no annotations and no output schema, the description covers the essential contract: what is created, what comes back, the sandbox/live distinction, and idempotency. Missing auth requirements and the exact live-mode gating (deferred to the schema) keep it from being fully self-contained.

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%, so the baseline is 3, but the description adds semantics beyond the schema: the default sandbox mode and the idempotency contract for external_id ('repeating an external_id returns the payment already created for it'). Those are behavioral facts the schema's field text does not convey.

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?

Specific verb+resource ('Create a Cryptunnel payment') plus the concrete outcome (checkout url) and the flow that follows (buyer picks a coin, pays to merchant's wallet). It also names the sibling it hands off to ('get_payment needs it'), so an agent can place it in the workflow without opening the schema.

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?

'Use it whenever someone has to be charged' gives a clear trigger condition, and the note about repeating external_id tells the agent how to handle retries. It never states when NOT to use it or how it relates to list_payments/list_currencies, so it stops short of full when/when-not guidance.

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