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

Description adds value beyond annotations by disclosing that paid tiers return PAYMENT_REQUIRED unless skipPriceCheck is set. Annotations indicate it's not read-only (readOnlyHint false), and description confirms mutation. However, it doesn't mention potential idempotency or what happens if the member is already enrolled in a tier.

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 sentences packed with essential information. No filler words. Front-loads the core action and immediately provides behavioral nuances and usage guidance.

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 tool with 3 parameters and an output schema, the description covers key behaviors (immediate vs payment), prerequisite (list_tiers), and parameter usage. No gaps for an AI agent to understand how to use it effectively.

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 description adds meaningful context: tierId can be omitted to enrol on default membership, and expiresAt is an optional ISO date to override expiry. This goes beyond the schema descriptions.

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?

Clearly states the verb 'Enrol' and resource 'member into a membership tier'. Distinguishes between free and paid tiers, and differs from sibling tools like get_membership_tier or list_tiers by focusing on the enrolment action.

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?

Explicitly says when to use: for enrolling members, with differentiation between free (immediate) and paid (may require payment). Provides a prerequisite: 'Use list_tiers first to find the target tier.' Also hints at an alternative (skipPriceCheck) to bypass payment requirement.

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