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

Annotations already indicate this is a write operation (readOnlyHint=false, destructiveHint=false). The description adds meaningful context by specifying 'non-renewing' and contrasting with provider-backed billing, but does not disclose further side effects or permissions. This extra context justifies a 4.

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 concise sentences with the verb and resource front-loaded. Every word earns its place, and the alternative guidance is packed efficiently. It is not verbose or over-specified.

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 8 parameters but full schema descriptions and an output schema, the description sufficiently covers the tool's key context. It clarifies the edge case of provider-backed recurring billing, though it doesn't explain the return value. This is complete enough for a tool with rich structured metadata.

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?

The input schema has 100% coverage, so the baseline is 3. The description does not add parameter details beyond the schema, but it reinforces the non-renewing nature (autoRenew const false). This meets the baseline but adds no extra semantic value.

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: 'Create a manual, non-renewing subscription record for a member.' This distinguishes it from provider-backed recurring billing, and the 'create' verb + resource is specific. It contrasts with sibling tools like create_plan_upgrade_link or enrol_membership.

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 explicitly gives an alternative usage: 'Use a subscription action link for provider-backed recurring billing.' This tells the agent when not to use this tool and points to a different approach, providing clear usage context.

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