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

Annotations already declare idempotentHint=true and destructiveHint=false, but the description adds the meaningful downstream effect: campaigns to that list (or every list) skip the address. That is the operational consequence an agent needs, and it goes beyond the structured fields. It stops short of noting permission requirements or behavior when the address is already opted out.

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, the core action front-loaded and the scoping nuance second. Nothing is wasted and no filler or restated title padding.

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 2-parameter tool with full schema coverage and annotations covering safety and idempotency, and with no output schema, the description supplies the effect of the write and the list scoping. The main gap is any distinction from the blocklist siblings.

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 100% and list_id's meaning ('Empty = every list.') is already documented in the schema, so the description's scoping sentence largely repeats it. Baseline 3 is appropriate since the schema carries parameter semantics.

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 ('Record an opt-out') that an agent can act on immediately. It does not, however, differentiate itself from the sibling 'block'/'list_blocklist' tools, which describe a closely related suppression concept, so the agent must infer the boundary.

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?

The description gives no when-to-use guidance and names no alternative; it never explains when an agent should call add_unsubscribe versus block or unblock. The list_id scoping rule is behavioral detail, not usage guidance.

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