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

Annotations already cover the read-only, non-destructive safety profile, so the bar is lower, and the description adds real domain behavior beyond them: buyers retain access while past_due, lose it on cancelled/incomplete/incomplete_expired, and Payhip auto-cancels after a 20-day failed-payment grace period. It also states the auth requirement (Cotlet API key with app access). It does not describe the return shape or pagination, which keeps it from a 5.

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?

Front-loads what the tool returns before adding lifecycle semantics and the auth note, and every sentence carries information. It is slightly dense but free of padding.

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?

No output schema exists, but the description covers what the tool returns, the plan types in scope, the status lifecycle semantics, and the credential requirement, which is sufficient for an agent to call it correctly. Nothing essential is missing given the annotations already carry the safety profile.

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 (email, limit, cursor, status) are already documented in the schema, making 3 the baseline. The description does add meaning to the status enum by explaining which values imply continued access versus loss of access, but says nothing extra about email, limit, or cursor.

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 (list) and resource (subscribers) and scopes it precisely to subscription, course, coaching and membership plans with status and start date. An agent can identify it as the subscriber-roster tool apart from payhip_list_orders or payhip_get_sales_report, though it never names those siblings explicitly.

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?

Usage is only implied by the purpose ('Subscribers to your ... plans'); there is no explicit when-to-use statement, no exclusions, and no routing to alternatives like payhip_list_orders or payhip_get_sales_stats. Adequate for a straightforward list tool but leaves the agent to infer the choice itself.

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