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

Annotations already provide readOnlyHint=true, so the read-only nature is covered. The description adds valuable context beyond annotations by specifying the REST endpoint (GET /lists/{list_id}/members/{subscriber_hash}), the email-to-MD5 hashing behavior, and the response contents (status, merge fields, tags, stats).

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 a single sentence plus a REST reference, front-loaded with the action and resource. Every clause adds value: the resource type, lookup methods, included fields, and the hashing mechanism. There is zero filler.

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?

With 3 parameters, no output schema, and readOnlyHint annotations, the description covers the core behavior, response contents, and hash conversion. However, it omits that subscriberHash can also accept a contact id (as noted in the schema), which is a minor completeness gap for a retrieval tool.

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%, so the baseline is 3. The description adds the REST path template and confirms that email is hashed to subscriber_hash, but this is duplicative of the email parameter's description. The subscriberHash parameter's ability to accept a contact id is present in the schema but not reinforced in the description.

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 starts with 'Get a single audience member (subscriber)', using a specific verb and resource that clearly distinguishes this tool from siblings like list_members or search_members. It also specifies the lookup modes (by email or subscriber_hash) and the included data fields, making the purpose unmistakable.

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 implies the tool is for retrieving a specific member by identifier but does not explicitly mention when to use this versus alternatives like list_members or search_members. There is no when-not-to-use guidance or named alternatives, which is a missed opportunity for clarity.

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