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

Annotations only declare the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false, openWorldHint=true); the description goes further by explaining that no charge occurs until the human completes checkout in a browser, that auth is required, and how the returned url must be handled. That is behavior beyond what the structured fields convey.

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 trigger condition, then the action, then constraints and inputs and return handling. Every clause is functional; there is 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 three-parameter checkout tool, the description covers trigger, prerequisite, mutation semantics (deferred charge), input roles, and the required post-call behavior. An output schema exists, so the brief return summary is a bonus rather than a necessity.

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 description coverage is 100% and the enum values (starter/pro) are already in the schema, so the description's parameter recap adds no new meaning. Baseline 3 applies when the schema carries the parameter documentation.

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 and resource: 'Creates a Stripe Checkout session', plus the trigger condition (human wants to upgrade / a limit was hit). It is clearly distinguishable from siblings like cooper_billing_status (status read) or cooper_set_addons (configuration change).

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 when-to-use conditions ('when the human wants to upgrade, or a limit was hit and they agree to pay') and an explicit downstream instruction: give the url to the human, never open or complete it yourself. It also flags the auth prerequisite, leaving little to inference.

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