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

The description adds behavioral context beyond the annotations by explaining the dual behavior (checkout vs portal) and the user-consent requirement. Annotations already indicate it's a write operation (readOnlyHint=false) and not destructive, which is consistent. However, it does not disclose side effects like whether it charges the user or sends email, though the schema mentions the confirm parameter, so partial coverage exists.

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?

The description is two concise sentences that front-load the main action and the usage condition. It contains no unnecessary filler or repetition, making it highly efficient and well-structured.

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?

Given the tool's moderate complexity (5 parameters, 0 required, output schema present), the description combined with the detailed schema and annotations is sufficient for an agent to understand when and how to invoke it. It clarifies the two use cases, the consent requirement, and the type of link generated. The output schema likely covers return values, so the description doesn't need to.

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?

With 80% schema description coverage, the baseline is 3. The schema already provides detailed descriptions for parameters like planId, confirm, planCode, returnUrl, and billingCycle, including important notes like 'Either planId or planCode is required' and 'confirm required true'. The description itself does not add parameter-level meaning beyond what the schema offers, so it stays at the baseline.

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?

The description clearly states the tool creates a Stripe Checkout link for new paid subscriptions or a Stripe Billing Portal link for existing subscriptions. It uses a specific verb ('Create') and identifies the exact resources, making it easy to understand what the tool does. It also distinguishes this from sibling tools by specifying the two use cases.

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 explicitly says 'Use only after the user explicitly asks to upgrade or fix billing,' providing a clear when-to-use condition. It also distinguishes between the two scenarios (new subscription vs existing subscription), which helps the agent choose the correct behavior. This is strong, explicit usage guidance even without naming alternatives.

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