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

The description goes well beyond annotations by explaining the Stripe checkout flow, the webhook that flips workspace to active, that compute unlocks automatically without agent action, and that past_due states return no checkout. It also explains the consequence of creating a new checkout for past_due (would create a second subscription). This is rich behavioral disclosure, and annotations (readOnlyHint false, openWorldHint true) don't contradict.

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 front-loaded with the core purpose and then provides detailed behavior. All sentences contribute to understanding: it explains the plan values, the checkout behavior, the webhook handling, and the past_due exception. While somewhat long, the length is justified by the complexity of the tool's behavior. No redundant or vague statements.

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 description explains the full flow: when checkout_url is returned, what to do with it ('send it to the user'), how payment completion works (webhook auto-unlock), edge cases (past_due, open-signup unpaid, churned, converting from free/trial), and it cautions against creating a duplicate subscription. Since an output schema exists (though not shown), not explaining return values is acceptable. The description is complete for an AI agent to understand when and how to invoke this tool.

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 only parameter 'plan' is documented in the description with the allowed values ('starter', 'pro', 'agency') and default ('starter'), which the schema lacks (0% coverage). This adds semantic meaning beyond the schema. It could have been slightly clearer about the effect of plan choice on checkout, but the allowed values and default are sufficient.

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 opens with 'Billing status + a Stripe checkout link when a NEW subscription is needed', clearly stating the tool retrieves billing status and returns a checkout URL only in new-subscription scenarios. It explicitly distinguishes from sibling tools (which are mostly project management) and specifies the resource (billing) and action (get). The mention of 'NEW subscription' narrows the scope, making it unambiguous.

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 provides explicit when-to-use and when-not-to-use guidance: it says the tool should be used when there is no live subscription and a checkout link is needed, and explicitly warns that for past_due workspaces one should not use this tool (follow next_step for card update instead). It also details the edge case of converting from free/trial, which helps the agent decide when to invoke it.

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