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

Annotations already declare the mutation is idempotent and non-destructive. The description adds only that the operation can subscribe or unsubscribe, which is largely conveyed by the 'subscribed' boolean in the schema. It does not disclose partial-update semantics, behavior when the subscriber does not exist, or 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?

The description is a single, front-loaded sentence with no filler. It is appropriately terse, although that terseness contributes to the gaps noted elsewhere.

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 7-parameter mutation tool with a nested object, low schema coverage, and no output schema, the description is too thin. It omits core update semantics and parameter guidance that an agent needs to invoke the tool correctly.

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 only 29% across 7 parameters, so the description should compensate but does not. It does not explain required 'id'/'subscriber_id', the optional email/name fields, or the nested 'custom_fields' object, leaving most parameters undocumented in both schema and 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 gives a clear verb and resource: 'Update a subscriber.' It also mentions the key capability of subscribing/unsubscribing. It is clear but does not differentiate from siblings such as add-audience-subscriber, remove-audience-subscriber, or bulk-update-audience-subscribers.

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?

There is no guidance on when to use this tool versus alternatives. The description does not explain whether to use it instead of add-audience-subscriber, remove-audience-subscriber, or the bulk-update variant, nor does it state prerequisites.

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