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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds real behavioral value by enumerating the verdict vocabulary (ok, invalid, no_mx, disposable, role), which tells the agent what kinds of outcomes to expect beyond what annotations convey.

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 short sentences, front-loaded with the purpose before the outcome vocabulary. Every clause earns its place and nothing is padded.

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 usefully discloses the return vocabulary (ok, invalid, no_mx, disposable, role), which is exactly what an agent needs to interpret results. It omits cost/quota or rate-limit context, but for a single-parameter read-only check it is largely complete.

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 description coverage is 100% for the single 'email' parameter, so the schema carries the parameter burden. The description's verdict list describes outcomes rather than the parameter, adding no syntax or format detail, so baseline 3 applies.

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 and resource ('Check an address') and a purpose timing ('before sending'), so the job is clear. However, it offers no differentiation from closely overlapping siblings like check_email, verify_check, and verify_start, leaving the agent to guess which check tool to pick.

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?

'before sending' implies a usage context, so guidance is present but only implied. There is no when-not guidance and no routing to or away from the multiple competing check/verify siblings, which is the biggest ambiguity here.

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