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 and repeat-call profile is covered structurally. The description adds only the 'subscribe' framing, and says nothing about what happens to contacts already subscribed, whether unsubscribed contacts are resubscribed, or any per-call error behavior.

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 no filler, and the batch limit is stated up front. Nothing is wasted, even if more could have been said.

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 full schema coverage and four annotations, the description is technically callable as written. But for a bulk mutation whose sibling bulk-resubscribe-contacts implies distinct resubscribe semantics, an agent cannot tell whether this tool handles previously unsubscribed contacts or errors on duplicates — a real gap left unaddressed.

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 100%: ids documents the con_xxx format and 100-item cap, and audience_id documents the aud_xxx format. The description's 'up to 100 contacts' simply restates maxItems, adding no new meaning; baseline 3 is appropriate.

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 (subscribe) and resource (contacts to an audience) plus the batch cap of 100, which distinguishes it from the single-contact add-audience-subscriber sibling. It does not name any sibling explicitly, so the differentiation is inferred rather than stated.

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 use this over add-audience-subscriber, bulk-update-audience-subscribers, or bulk-resubscribe-contacts. The only hint is the '100 contacts' cap, which is already in the schema's maxItems, so the description provides no routing logic.

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