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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this call mutates nothing. The description adds real context beyond that: the payment occurs on a Stripe page with card/Apple Pay/Link, and 'Agents never enter card details' draws a clear safety boundary. It stops short of stating auth or expiry characteristics of the link.

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?

Three short sentences, each earning its place: what it returns, what happens next at the payment step, and which sibling to prefer. The return value is front-loaded and the routing advice closes it.

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, and the description compensates by stating the return is a link and explaining the downstream payment flow. Safety behavior is covered for a read-only tool. Coverage is nearly complete; only link lifetime/expiry behavior is unaddressed, which is minor.

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?

One optional parameter with a two-value enum and 100% schema description coverage, so the schema fully documents it. The description's mention of 'monthly or yearly' echoes the enum but adds no format or default nuance beyond 'Default month' already in the schema. Baseline 3 applies.

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 — returns the payment link for Elite — and scopes it to monthly or yearly billing. It explicitly distinguishes itself from the sibling start_trial, so an agent can route correctly without opening the schema.

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 routing guidance: 'Most people should start with start_trial instead.' That names the alternative and the default path. It also clarifies the human-in-the-loop condition (payment happens after the person signs in).

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