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

Goes beyond annotations by disclosing the credit cost, which is critical for an agent deciding whether to call this repeatedly; this is consistent with readOnlyHint=false. It also enumerates the possible result values, useful given there is no output schema, though it omits latency/escalation differences between fast and full checks.

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 with the deliverability check front-loaded, followed by result values and cost. The result enumeration is lengthy but earns its place because no output schema exists.

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 two-parameter tool with no output schema, covering result values is the right call, and credit cost is disclosed. What is missing is how 'mode' affects the meaning or confidence of the returned status (e.g., 'unknown' in fast vs full), which an agent needs to interpret results 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 50%: the 'mode' parameter is well documented in the schema itself, and 'email' is self-evident as the single required input, so the description needn't repeat them. However, the description never mentions that 'mode' changes what is checked, so it adds nothing to parameter understanding.

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?

States a specific verb ('Check') and a specific resource scope ('one address is deliverable'), which distinguishes it from the sibling verify-domain (domains) and from list-based verification tools. It is not fully explicit about sibling differentiation, but 'one address' does the disambiguating work.

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?

There is no guidance on when to use this versus verify-domain, create-verification-list, or bulk verification flows, and no mention of preconditions (e.g., whether the address needs to exist in the workspace first). Usage is only inferable from the purpose statement.

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