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

Annotations already declare the safety profile (not read-only, non-destructive, idempotent), so the description's main addition is the consent precondition, which is genuinely useful for a compliance-sensitive write. The 100-item cap is repeated from the schema's maxItems, and nothing is said about partial failures or what happens to IDs that weren't unsubscribed.

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 with zero filler; the what (resubscribe, cap) is front-loaded and the consent rule follows as the gating condition.

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 one-parameter bulk mutation with full schema coverage and annotations covering safety, the description supplies purpose, limit, and precondition. The only residual gap is outcome behavior (partial success, unknown IDs), which is minor given there's no output schema.

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 the single 'ids' parameter is documented as 'Contact IDs (con_xxx), up to 100.' The description's 'up to 100 contacts' restates the schema constraint without adding syntax or format guidance, so this sits at the baseline.

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 ('Resubscribe ... contacts') plus the bulk cap of 100, which is enough to separate it from bulk-unsubscribe-contacts and the audience-subscriber siblings. It doesn't explicitly name a sibling to steer away from, but the operation is unambiguous.

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?

Adds an explicit precondition — 'Only do this when they asked to receive email again' — which tells the agent when this tool is appropriate. It stops short of naming when-not conditions or alternatives (e.g., for contacts who never unsubscribed), so it's clear context rather than full routing.

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