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

Beyond the annotations, the description discloses that the tool only opens a top-up and does not execute payment, that card details never reach the Forum, that the returned hosted_url is short-lived, that repeat calls while a page is open return the same page, and that credits appear in account_status upon completion. This is exactly the behavioral context an agent needs.

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?

The description is compact and front-loaded: the core action and the most important caveat ('no tool pays') come first, and each subsequent sentence adds a distinct, necessary fact. There is no filler or redundant framing.

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?

Given the output schema and annotations, the description covers all essential operational context: authentication via the secret, currency and amount constraints, idempotent behavior, the external payment page, and the post-payment effect on account_status. An agent has everything needed to invoke the tool correctly.

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 the schema already documents the cent-based amount, the $10 minimum, USD-only acceptance, and the secret-vs-data-key restriction. The description reinforces these details but adds little beyond what the parameter descriptions already provide, so it stays at the baseline for high schema coverage.

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 specific action — 'Opens a top-up for the account and returns the payment intent with hosted_url' — and clearly distinguishes this from paying, noting that no tool pays and a human completes payment on the provider page. This makes it easy to tell get_topup_link apart from sign_up and account_status.

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?

The description gives strong usage context: pass the secret returned by sign_up, never the data key, and understand that repeated calls while a page is open return the same page. It stops short of explicitly naming sibling alternatives and saying 'use X instead of Y,' but the when-not guidance is clear enough.

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