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

Beyond the readOnly and openWorld annotations, the description discloses cost (1 credit), the scam-list check, and an important output privacy constraint: existence and status only, never the person's name. These are meaningful behavioral details an agent would otherwise not know.

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 sentences, front-loaded with the core existence/status question and then the privacy and cost constraints. Every sentence adds useful information with no repetition or 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?

With an output schema and annotations already present, the description supplies the remaining decision-relevant context: cost and privacy limitations. It is complete enough to invoke correctly, though it could mention pagination or rate-limit behavior if applicable.

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 description coverage is only 50%, but the description compensates by naming the supported providers and the handle formats ($Cashtag, PayPal.me name, Venmo username). It reinforces the provider enum and handle semantics beyond the schema text.

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 precise lookup operation across named payment providers and specifies the exact checks performed: existence, active status, and scam-list membership. It distinguishes this tool from adjacent lookups like lookup_email or lookup_wallet by naming Cash App, PayPal.me, and Venmo.

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 payment-handle domain makes usage broadly clear, but the description does not explicitly say when to use this tool versus other lookup_* siblings or when not to use it. It implies usage through the provider names without offering alternative routing or exclusions.

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