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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real context beyond them: no input required, an empty list means there are none, an unlinked account returns an error prompting sign-in, and these schedules never take automatic card payments. It also explains that the returned id is what change_subscription consumes, which is genuine cross-tool behavioral information.

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-loaded with the trigger condition and the primary payload, then the edge cases and the hand-off to change_subscription. It is denser than strictly necessary, but each sentence carries distinct operational information rather than 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?

An output schema exists, so return-format detail is unnecessary; the description instead supplies the things the schema cannot: the sign-in prerequisite, empty-list semantics, payment-model caveat, and the id contract with change_subscription. Nothing an agent needs to invoke this 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?

There are zero parameters and the schema is fully self-describing, so the baseline is 4. The description confirms the no-argument nature ('It takes no input'), which is accurate but adds little the empty schema did not already convey.

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 and resource (lists every subscription on the linked account) plus exactly what each entry conveys: what it sends, frequency, next delivery, price, active/paused status. It is immediately distinguishable from change_subscription, which it names as the mutation counterpart.

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?

Explicitly scopes the trigger ('when a signed in customer asks about their ... subscriptions') and routes the pause/resume/cancel cases to change_subscription by name. It also covers the no-linked-account failure path, so the agent knows the expected outcome in that condition.

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