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

With no annotations, the description carries the full burden, and it does add real value: it discloses the return (a unique USDT amount + address) and the auto-activation behavior on exact payment. It omits key behavioral facts such as whether the quoted amount expires, idempotency/retry behavior, or what happens if the wrong amount is sent.

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, front-loaded with the action and immediately followed by the outcome. Every clause earns its place with 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?

For a no-annotation, no-output-schema payment-initiation tool, the return value is covered, but the description never mentions the human-confirmation requirement baked into the required user_confirmed flag, nor amount expiry or failure modes. It is adequate but leaves meaningful gaps for a tool handling payment.

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?

All 4 parameters are required and schema description coverage is only 25% (only user_confirmed is described). The description explains nothing about plan_code, email, or agent_id, so it fails to compensate for the coverage gap on a tool where every input is mandatory.

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 concrete verb+resource ('Open a payment for a plan') and even describes the resulting effect, which is more than a name restatement. It doesn't explicitly distinguish itself from purchase_quote or purchase_status, so it falls short of a 5.

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?

Usage is implied by the flow ('send that exact amount and the subscription starts by itself'), which tells the agent this is the initiating step of a payment sequence. There is no explicit when-to-use versus purchase_quote/purchase_status guidance or any stated prerequisite beyond what the schema forces.

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