check_domain

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

With no annotations provided, the description carries the burden of behavioral disclosure. It states that the tool verifies MX records and returns mail server details, and adds the important trait that it does not count against verification quota. This covers the core behavior, though it could mention failure/success signaling more explicitly.

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 two sentences, front-loaded with the primary purpose, then the mechanism, followed by usage guidance and a quota note. Every sentence earns its place with no redundancy.

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 one-parameter tool with no output schema, the description covers the purpose, usage, and key behavioral trait (no quota). It mentions 'returns mail server details' which gives a sense of the output, though a bit more detail on the return format would be beneficial.

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?

The schema covers the single parameter 'domain' with a type, description, and example. Schema description coverage is 100%, so the description adds no additional parameter semantics. Baseline 3 is appropriate.

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 clearly states the tool checks if a domain can receive email by verifying DNS MX records, and explicitly distinguishes it from email verification tools by noting it does not count against verification quota. This differentiates it from siblings like verify_email and find_emails.

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 explicitly says to use this tool 'to filter out dead domains before running find_emails', providing a concrete when-to-use scenario. It also implies a lightweight pre-screening role ('Quick check') and notes quota savings, but does not explicitly name alternative tools for other cases.

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