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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds that returned records include plan, start date, and activity rating, which is useful return-shape context, but it does not explain pagination via cursor/limit or ordering. With annotations covering the safety profile, a 3 is appropriate.

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?

It is short with no wasted words, but it is a fragment rather than a front-loaded statement of purpose. Brevity here comes at the cost of specification, not from efficiency.

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 paginated list tool with no output schema, the description should at least signal pagination behavior and what a subscriber record contains. It gestures at return fields but says nothing about paging, total counts, or scope, leaving significant gaps.

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 all four parameters (plan enum, limit, since, cursor) are already documented in the schema, including defaults and ranges. The description adds only loose references to plan and start date and nothing about cursor/limit semantics, so the baseline 3 is correct.

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 is a noun fragment ('Subscribers with plan, start date and activity rating') that restates the tool name and lists fields rather than stating what the tool does. It does not distinguish list_subscribers from close siblings such as list_subscriptions, export_subscribers, or list_subscriber_tags, so an agent must infer that this is the paginated subscriber listing.

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 export_subscribers, list_subscriptions, or list_subscriber_tags, and no mention of prerequisites or exclusions. Usage is only implied by the name.

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