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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=false and idempotentHint=false, so the safety profile is covered. The description adds the delivery-blocking consequence, but says nothing about what happens on a duplicate address — which matters given idempotentHint=false — nor about required scopes/permissions or the returned record.

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 front-loaded sentence with zero filler, which is the right shape for a simple create tool. It is arguably too terse given the undocumented parameters, but nothing in it is wasted.

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 four parameters at 25% coverage, no output schema, and a non-idempotent mutation, the description would need to explain the type values, duplicate behavior, and what gets created. None of that is present, so a caller cannot be confident it will invoke the tool correctly.

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 only 25%: keep_until is documented in the schema, while email, reason and the type enum (recipient/bounce/complaint/unsubscribe) carry no explanation anywhere. The description compensates for none of this, so an agent must guess what each suppression type means and what reason is used for.

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 (add) and resource (suppression list) plus the concrete effect: Emailit will never send to that address. That is clear enough to distinguish it from get-suppression or delete-suppression by name alone, but the description never names those siblings explicitly, leaving the routing to inference.

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 guidance on when to call this versus update-suppression (e.g. changing an existing suppression's expiry) or the bulk unsubscribe/contact tools. The only usage signal is the implied 'add an address that should never be mailed', which is context rather than a decision rule.

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