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

Annotations mark this non-read-only and open-world, but the description adds the crucial cost trait ('Consumes 1 credit') that annotations cannot express, plus the enumerated verdict domain (deliverable / risky / undeliverable / unknown). It does not mention latency or rate limits, but the credit disclosure is a real value-add.

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 tight sentences: capability/scope first, then return contract and cost. Every clause earns its place with no filler or repetition of the title.

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 no output schema, the description does supply the verdict vocabulary an agent needs to branch on. It stops short of describing the remaining payload (e.g. typo suggestion text, MX records) and there is no output schema to fill that gap, but the primary decision surface is covered.

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?

There is one parameter at 100% schema description coverage ('The email address to verify'), so the schema already carries the semantics. The description adds nothing about accepted formats or normalization, which is the baseline expectation at this coverage level.

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 names a specific verb and resource ('Verify a single email address') and enumerates the exact checks performed (syntax, domain/MX, disposable, role, typo, mailbox reachability). The word 'single' cleanly separates it from the bulk siblings verify_emails and verify_list without opening their schemas.

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?

Usage is implied: pick this when you need a full deliverability verdict on one address. However, it never says when to prefer a narrow sibling like check_domain, check_disposable, or check_typo, nor when to escalate to verify_emails for batches, leaving the agent to infer the boundary.

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