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

Annotations already declare this is a non-readonly, non-idempotent, open-world, non-destructive mutation, so the safety profile is covered. The description adds only that the customer completes checkout, which implies an external handoff (consistent with openWorldHint) but says nothing about side effects like creating subscriptions, expiry of links, or repeat invocations generating duplicate links.

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 short sentences, with the core action front-loaded and no filler. The second sentence adds a little flow context but is close to redundant given the tool name.

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?

The tool is simple (one param) and has an output schema, so return values need not be explained. However, an agent still lacks where valid plan IDs come from, what the returned link's lifecycle is, and how this differs from create_billing_portal — gaps that matter for correct invocation.

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?

The single 'plan' parameter has 0% schema description coverage, so the description carries the burden; 'current plan ID' does clarify that the string must be an existing plan identifier, but gives no format, source, or validity rules. That is marginal help over an undocumented string.

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 ('Create a checkout link') and ties it to a plan ID, which is enough to separate it from read-only siblings like get_plans. It stops short of distinguishing it from the closely related create_billing_portal, so it is clear but not fully differentiated.

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 customer completes checkout' hints at the flow (you hand the link off), but there is no explicit when-to-use guidance, no prerequisites (e.g. obtain the plan ID via get_plans), and no mention of when to prefer create_billing_portal instead. Usage is only implied.

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