Pay: entitlement

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered; the description reinforces "Read-only" and, with no output schema, usefully enumerates the returned fields (status, trial end/days left, subscription id, provider, product, expiry). It stops short of details like freshness or caching, but adds solid context beyond the annotations.

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?

Three tight sentences, front-loaded with the core purpose before the return payload and the alternative-tool pointer. No filler or 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?

For a zero-param read tool with no output schema, the description supplies everything needed: identified subject, enumerated return fields, read-only nature, and a routing hint to the sibling for other users. Nothing an agent needs to call it correctly is missing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The scoping statement ("the one this tool runs as") correctly signals that no subject argument is accepted.

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 action ("Show"/"Reports") on a precise resource (the signed-in user's paid or trial entitlement) and enumerates the reported fields. It is trivially distinguishable from the many pay_* siblings because it explicitly scopes to the current user.

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?

Gives an explicit alternative and the condition that selects it: "To look up another user, use `pay_subscriptions_by_user`." The current-user scope is clearly implied, but it does not distinguish itself from close siblings like pay_status, pay_trial_status, or pay_subscriptions_check_access, so guidance is strong but not complete.

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