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

The only annotation is destructiveHint=true, so the description carries most of the burden and does so well: it discloses partial-patch semantics and that email/phone entries are ADDED rather than replacing existing values. It does not explain merge-vs-replace behavior for custom_fields or any permission requirements.

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?

Four short sentences, zero filler, with the most important constraint (partial update) and the unusual additive/additive/coupling behaviors front-loaded ahead of the API endpoint reference.

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 9-parameter mutation with no output schema, the description covers the non-obvious semantics well. Minor gaps remain on permission/auth requirements and how custom_fields values merge, but nothing essential to invoking it correctly 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?

With 100% schema coverage the baseline is 3, but the description adds real meaning beyond the schema: the additive nature of emails/phones and the cross-parameter dependency that custom_fields requires membership_type. That coupling is the key operational detail an agent needs.

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 and resource ('Update fields on an existing member'), and 'existing' implicitly separates it from the sibling create_member. It does not explicitly name or contrast with update_opportunity or other siblings, so it stops short of full differentiation.

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?

Gives clear operating context: only passed fields are sent (partial update), emails/phones are additive, and custom_fields updates require membership_type. No explicit when-not-to-use or alternative-tool routing is provided, so it is strong but not complete.

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