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

With no annotations the description carries the full burden, and it does real work: it discloses the DNS-over-HTTPS mechanism, explicitly rules out SMTP probing (so mailbox existence is not verified), and states the cost ('Uses 1 check'). It stops short of covering auth requirements, error behavior, or return shape.

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?

A single dense sentence, front-loaded with the verb and resource, followed by the enumerated checks and two short constraint clauses. No filler and 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?

No output schema exists, so the description should say what comes back — a boolean, a score, or per-check results — and it does not, despite listing the individual signals it computes. It is otherwise adequate for a single-parameter read-style tool with no annotations.

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?

One required parameter with 0% schema description coverage. The description implies the input is a raw email string to be checked, but adds no format, normalization, or length guidance beyond that obvious inference, so it only marginally compensates for the empty schema.

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 resource (email address) and enumerates exactly which checks are performed: syntax, MX/A records, disposable domain, role address, free provider, typo suggestion. The resource alone distinguishes it from the only sibling, validate_phone.

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 explicit when-to-use statement, no routing to or away from validate_phone, and no stated preconditions. The scope note 'No SMTP probing' hints at what kind of validation result to expect, but it is a behavioral boundary rather than usage guidance.

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