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

Annotations only give generic hints (not read-only, not destructive, not idempotent); the description adds the crucial behavior that blocked addresses receive zero email including transactional, and that the state persists until unblocked. It stops short of saying what happens on a duplicate block (error vs. no-op) despite idempotentHint=false, which is the remaining gap.

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; the destructive scope is front-loaded and the alternative follows. Every clause carries information 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?

For a three-required-parameter mutation with no output schema, the description conveys effect, scope, duration, and the correct alternative. Only edge-case behavior (duplicate blocks, validation errors, interaction with existing consent records) is left unstated.

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% — only "reason" is documented there — so the description must compensate. It partially does by framing the effect as scoped "from this project," implying project_id narrows the block, but it adds no guidance on the email format or on whether reason may be null.

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 ("Block an address") and immediately defines the exact scope of the effect: no email at all, transactional included, until unblocked. It also names the sibling it is not (unsubscribe_email), so an agent can distinguish it without opening either schema.

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?

Explicitly routes the agent: use this tool for a full block, but use unsubscribe_email when the person only wants no marketing email. That is a clear when-to-use / when-to-use-something-else rule, plus the implied reversibility path (unblock_email).

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