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

Annotations already declare openWorldHint=true, idempotentHint=false and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior: the call returns a PayPal URL where the end user must approve, meaning the subscription is not active on return. It omits that repeat calls create additional subscriptions (non-idempotent), which would be the natural complement to that hint.

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 short sentences: purpose, parameter choice, return behavior. Front-loaded and free of filler, with each sentence carrying distinct information.

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 one-parameter tool with no output schema, the description covers what it does, the allowed values, and what comes back (a PayPal approval link). What is missing is minor but real: prerequisites for the approval step and whether a created-but-unapproved subscription lingers.

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 coverage is 0% for the single parameter, which is a bare untyped string with only a default of "monthly". The description compensates by enumerating the accepted values (monthly or yearly), information found nowhere in the schema. A case-sensitivity note or confirmation of the default would push this to a 5.

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?

"Skapa en PayPal-prenumeration för ARN Konsumenttvist" gives a specific verb (create) plus a specific resource (PayPal subscription) tied to a named service. It is clearly distinguishable from the sibling arn_cancel_subscription by implication, though that sibling is never explicitly named.

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?

The description says to choose monthly or yearly, which is parameter guidance rather than when-to-use guidance. It implies the flow (create link, user approves) but never states prerequisites such as a PayPal account, nor when to prefer this over the cancel sibling.

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