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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses pricing, payment rail, that failed calls are not charged, and the important false-negative caveat. These are meaningful behavioral details an agent needs before invoking the 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?

The purpose is front-loaded, followed by the key limitation and then pricing. Every sentence adds useful information without waste.

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 simple read-only blocklist lookup with an output schema, the description covers purpose, limitations, pricing, and invocation constraints sufficiently. Nothing essential is missing.

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 schema already documents the single email parameter. The description adds real semantic value by clarifying that either an email or a bare domain may be supplied and that only the domain portion is ever checked.

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 verb and resource: checking an email address's domain against a disposable/temporary email blocklist. It adds concrete scope such as the approximate list size and clarifies that only the domain, not the mailbox, is checked, which distinguishes it from generic email or domain 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?

It clearly indicates the usage context: checking whether a domain is known-disposable, with the caveat that absence from the list is not proof of permanence. It does not explicitly name alternative tools or state when not to use it, so it falls short of full routing guidance.

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