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

The description discloses that the tool returns a URL for human browser payment, implying no immediate charge. Annotations (readOnlyHint=false, openWorldHint=true) already indicate a write operation with external effects. The description adds context about the payment flow but doesn't detail idempotency or error states. No contradiction with annotations.

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 short sentences, front-loaded with the core action and purpose. Every sentence adds value: what it does, what it returns, and how it's used. No wasted words.

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 presence of an output schema (not shown), the description appropriately explains the key return value (a URL) and the overall user flow. It's complete for a tool that initiates a payment session, though it could mention session expiration or webhook callbacks.

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 100% with good descriptions for both parameters. The description adds minimal extra meaning beyond the schema, only hinting at 'upgrading or purchasing' to contextualize plan_slug. Baseline of 3 is appropriate as the schema does the heavy lifting.

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 explicitly states the verb 'create', resource 'Stripe Checkout session', and purpose 'upgrading or purchasing a plan'. It distinguishes from sibling tools like billing.get_portal and billing.list_plans by clearly focusing on the payment initiation step.

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 clearly indicates when to use this tool (for human payment via Checkout), but it does not explicitly mention when not to use it or point to alternatives like billing.get_portal for subscription changes. The context is clear but lacks exclusions.

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