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

The description says 'Safe to repeat — an order is captured at most once,' which asserts idempotent behavior, but annotations set idempotentHint=false. This is a direct contradiction on a safety-relevant trait, so the score is 1. It otherwise adds useful context about credits being added, balance returned, cost, and account requirements.

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?

Three short sentences, front-loaded with the trigger and effect, then safety, cost, and auth. It is appropriately sized and has 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?

Covers the critical context: when to call, what changes, the return value, cost, and account requirement. However, the incorrect idempotency claim undermines completeness for a mutating capture tool with no output schema, leaving a clear trust 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?

There is only one parameter, order_id, and schema coverage is 100%; the schema already states that it is the order_id returned by buy_credits. The prose does not add syntax or validation details beyond the schema, so baseline 3 applies.

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?

Names the specific operation (capture an approved PayPal order) and the outcome (pack credits added, new balance returned), and ties it to the preceding buy_credits step. This clearly distinguishes it from sibling tools.

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 states the trigger condition: call after the user approves the buy_credits link on PayPal, which clearly routes the agent from buy_credits to confirm_credit_purchase. It does not specify failure or expiry cases, so it is not a full 5.

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