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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false; the description adds that the effect is permanent within these tools and that it suppresses future campaign sends, which the annotations do not convey. The additive-blacklist semantics are consistent with destructiveHint=false rather than contradicting it.

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 operation type is front-loaded in a 'WRITE:' prefix, followed by effect, durability warning, and endpoint. No filler.

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 3-parameter mutation with annotations but no output schema, the description covers what it does, permanence, and side effects on campaigns. It leaves unspecified what happens if both email and phone are omitted and what the response contains, minor gaps given the tool's simplicity.

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 blacklist_id is documented), but the description compensates by explaining that 'email and/or phone' are the identifying values — implying at least one is required while neither is schema-required. That is real meaning beyond the schema, though it does not specify precedence when both are supplied.

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 email and/or phone as unsubscribed in a blacklist'), names the downstream effect ('campaigns using that blacklist skip it'), and gives the endpoint. It is clearly distinguishable from siblings like sarbacane_list_blacklist_entries and sarbacane_upsert_contact.

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 leading 'WRITE:' tag plus the unsubscribe framing gives a clear condition for use, and 'Cannot be undone with these tools' signals the caution needed before calling. It does not explicitly name an alternative (e.g. listing existing entries first) or state when not to use it, so it stops short of 5.

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