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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds real context beyond them: no input required, full-account listing (no filtering), empty list semantics, an error path when no account is linked, and the fact these are schedules that never take automatic card payments.

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, then scope, then semantics, then the alternative. Dense but every clause (empty list, error case, no card payments, sibling routing) earns its place.

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 no-param read tool with an output schema, the description covers everything an agent needs: what triggers it, what it returns in aggregate, the empty and unauthenticated cases, and the id handoff to change_subscription.

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?

Zero parameters, so the baseline is 4. The description confirms 'It takes no input,' which aligns with the empty schema, but there is no additional parameter meaning to 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 the exact fields returned (what each sends, how often, next delivery, price, active/paused). It is unmistakably distinguishable from sibling tools like my_orders or change_subscription.

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 usage to 'when a signed in customer asks about their teas.co.uk tea subscriptions' and routes mutation intent away with 'To pause, resume or cancel one use change_subscription.' Both the when and the when-not are stated directly.

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