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

Adds substantial context beyond annotations: requires auth, no charge occurs until the human completes checkout in the browser, the return shape {url, session_id, plan}, and the required hand-off behavior. Annotations confirm the idempotency/read-only profile, but the description supplies the operational cautions.

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 when-to-use condition, then requirements, then inputs, then return/hand-off. Every sentence carries actionable information with 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?

No output schema exists, yet the description names the returned fields and instructs what to do with the url. Combined with full parameter coverage and annotations, nothing needed to invoke this tool 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?

Schema coverage is 100% and the schema already documents plan (with enum), email, and client_id. The description largely restates these with only marginal added meaning (idempotency intent), so it earns the baseline 3 rather than more.

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?

Specific verb+resource: creates a Stripe Checkout session for upgrading a plan. It clearly distinguishes itself from billing/status siblings like cooper_billing_status, and states the artifact produced (a checkout url the human must complete).

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?

Gives explicit trigger conditions ('when the human wants to upgrade, or a limit was hit and they agree to pay') and an explicit boundary ('never open or complete it yourself'), which tells the agent precisely when and how to act versus deferring to the human.

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