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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description usefully adds the actual effect ('sends to it are refused'), but says nothing about reversibility, whether already-queued mail is affected, or auth requirements.

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, zero filler, with the action and its effect front-loaded. Nothing could be trimmed without losing information.

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 3-parameter mutation with rich annotations and no output schema, the description covers purpose, scope and consequence. The remaining gaps (the 'reason' parameter and behavior on duplicate/invalid values) are minor but real.

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 only 33%: 'value' is documented and 'kind' is an enum, but 'reason' is unexplained in both schema and description. The description's 'email address or a whole domain' partly compensates by mapping to the kind enum, but it adds no syntax, format, or meaning for the undocumented parameter.

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?

Specific verb (block) plus the two resource types (email address or whole domain) and the account scope. It is clearly distinct from the obvious sibling 'unblock', but it never names or contrasts with any sibling, so it stops short of full differentiation.

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?

'Sends to it are refused' implies the use case (stopping inbound mail) but gives no explicit when-to-use/when-not guidance and never points to list_blocklist or unblock for inspection/removal. Usage is inferable rather than stated.

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