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

The description adds meaningful behavioral details beyond annotations: free tiers enrol immediately, paid tiers return PAYMENT_REQUIRED unless skipPriceCheck is set. This is not evident from readOnlyHint=false or other annotations. It could mention side effects or idempotency, but the openWorldHint and destructiveHint already set expectations, so the added payment behavior is valuable context.

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?

The description is three sentences long, front-loaded with the core purpose, and each sentence provides essential information: the action, the payment behavior, and the prerequisite. There is no fluff or redundancy.

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?

Given the output schema exists, return values are already covered. The description covers the main behavioral aspects (free/paid tiers) and the prerequisite (list_tiers), but the reference to skipPriceCheck without a corresponding schema field leaves a minor gap. Overall, it is complete for a tool of this complexity.

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 baseline is 3. The description does not add additional meaning to the listed parameters (tierId, accountId, expiresAt) beyond what the schema already provides. The mention of skipPriceCheck is a behavioral condition not tied to any schema property, which creates slight ambiguity but does not clarify parameter usage.

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?

The description clearly states the tool's purpose with a specific verb and resource: 'Enrol a member into a membership tier.' It distinguishes itself from sibling tools like list_tiers and get_membership_tier by focusing on the action of enrolment, and the mention of 'membership tier' differentiates it from subscription-related tools.

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 explicit context for when to use this tool: 'Use list_tiers first to find the target tier' and explains the free vs paid tier behavior. It does not explicitly name alternative tools (e.g., create_subscription) or state when not to use it, but the prerequisite and payment caveat provide clear usage guidance.

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