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

The annotation already provides destructiveHint=true, and the description adds valuable behavioral details: partial update semantics ('Only the fields you supply change') and the email-to-MD5-hash transformation. This goes beyond the annotation without contradicting it.

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 extremely concise, with three short sentences that front-load the action and add only relevant details: action, partial-update behavior, and REST endpoint/hash context. Every sentence earns its place with no 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?

The description is complete enough for this tool's complexity. It covers purpose, identification, partial-update behavior, and endpoint. While there is no output schema to explain return values, that is not essential for invoking an update tool; required parameters are already documented in the schema.

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 adds extra meaning by clarifying the partial-update behavior, which applies to all optional parameters. This is not explicitly stated in the schema descriptions and helps the agent understand parameter semantics.

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 action ('Update'), the specific resource ('existing audience member'), and the means of identification ('by email or subscriber_hash'). It distinguishes itself from sibling tools like add_member and archive_member by explicitly targeting existing members for modification.

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 clearly implies use for updating existing members rather than adding or archiving. It provides contextual guidance that only supplied fields change, which helps the agent decide when to use this tool. However, it does not explicitly name alternative tools or state when not to use it.

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