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

Annotations only say it's a write (readOnlyHint=false, destructiveHint=false, openWorldHint=true). The description adds real value beyond that: it 'reaches money' because billing follows the membership type, it documents the confirmation default, and it names the required Cotlet API key scope. This is substantive behavioral disclosure.

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?

Front-loaded with the purpose, but redundant: 'Add a membership to a member / Billing follows the membership type' is repeated by 'Adds a membership to a member from a given start date / Billing then follows the terms...'. Two of the sentences restate the first pair, so it is longer than it needs to be.

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 money-impacting mutation with no output schema, the description covers the important non-schema facts: monetary effect, confirmation policy, and auth scope. It stops short of error/renewal behavior, but nothing critical for correct invocation is missing.

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 person_id, membership_type_id and start_date (with its 'Default: today'). The description only restates the start-date concept and adds no syntax or constraint detail, so baseline 3 applies.

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+resource: 'Add a membership to a member', then clarifies that billing follows the membership type. The purpose is unambiguous and distinct from siblings like get_member or promote_rank, though no sibling is named for contrast.

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?

Usage is only implied (use it when you want to attach a membership). The confirmation policy ('By default you confirm each call; you can switch that off') is guidance about invocation behavior, not about when to choose this tool versus an alternative, and no alternatives or exclusions are given.

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