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

Annotations already declare readOnlyHint=false, destructiveHint=true and openWorldHint=true, so the mutation risk profile is covered structurally. The description adds beyond that: it explicitly labels the call a WRITE, discloses the verified-subscriber constraint, and warns that an already-promoted subscriber returns an error. The only mildly confusing point is that idempotentHint=true while re-promotion errors, but the description does not contradict the annotations outright.

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?

Three tight sentences: operation class first, then constraint and error behavior, then endpoint. No filler, no repetition of the title, and the most decision-relevant information is front-loaded.

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, fully-required mutation with no output schema, the definition covers what it does, the eligibility gate, and the failure mode. The main omission is what a successful response looks like and whether promotion is reversible (demote path), which an agent might want before calling a destructive tool. Annotations and the confirm parameter partially compensate.

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%, so the schema already documents uuid format, subscriber_id format, and the meaning of the confirm gate including its side effects. The description adds no parameter-level detail of its own beyond echoing the path shape. Baseline 3 applies when the schema carries the 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?

Specific verb ('promote') plus target resource ('subscriber to the campaign's winners list') and a scoping parenthetical clarifying it applies to contests and giveaways. The 'WRITE:' prefix immediately signals the operation class, and the endpoint path reinforces the resource hierarchy. An agent can distinguish this from read-side siblings like get_subscriber or list_subscribers without opening the schema.

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 valuable preconditions: only verified subscribers can be promoted, and re-promoting errors out. But it offers no guidance on when to choose this versus nearby mutating siblings such as unlock_promoted_reward or update_subscriber, nor does it say when in a workflow promotion is appropriate. Usage is implied by the precondition rather than stated as routing guidance.

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