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

With no annotations, the description carries the full burden and does well: it discloses that a human must open the link (not an API-callable action), that cancellation preserves Pro through the paid period, that names are never deleted, and the 409 failure mode. It stops short of stating auth scopes or link expiry, but the behavioral surface is unusually well covered.

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?

Two dense sentences, front-loaded with what the tool returns and what it is for, then the constraints and error path. Every clause carries information; no 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?

For a zero-parameter, no-output-schema tool, the description covers the return value (portal link), the human-in-the-loop requirement, side-effect semantics of cancellation, and the error route to the sibling tool. Nothing an agent needs to select or invoke 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?

Zero parameters, so there is nothing to document and the baseline is 4. The description correctly does not invent parameter guidance.

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 (get) and resource (Stripe billing-portal link) and enumerates exactly what the portal enables: update card, view invoices, switch billing cadence, cancel. It also distinguishes itself from the sibling upgrade_to_pro by naming the 409 case that routes there.

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?

Explicit when-to-use (pro account billing self-service), an explicit constraint ('a human must open it'), and an explicit alternative for the edge case: 409 if the account has never subscribed, use upgrade_to_pro. Nothing is left to inference.

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