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

Adds substantial behavior beyond annotations: no charge on preview, charge only after the user pays on Stripe, and that confirming with an active add-on redirects to billing rather than purchasing. This discloses the financial safety model that the destructiveHint=true annotation alone would leave ambiguous.

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 verb and the plan codes, then the confirm workflow. Dense but nearly every sentence carries necessary billing-flow detail; a touch long but hard to cut without losing safety context.

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 destructive, open-world billing mutation with no output schema, the description covers the full workflow, permissions, pricing, the money-movement timing, and the already-active edge case. An agent has everything needed to invoke it correctly.

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% so the schema already documents each parameter, but the description adds real value: it enumerates plan codes with their prices/quantities and explains that expected_plan_code, expected_price_usd, and expected_addon_status all come from the preview call. Slightly short of 5 because expected_addon_status usage could be clearer.

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 ('Buy an X posting add-on') and is clearly distinguishable from siblings like get_x_posting_quota (read allowance) and upgrade_subscription. An agent can tell what this does 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?

Explicit two-phase workflow: call without confirm for a preview, show the price, then call with confirm=true plus the expected_* fields. Names the active-add-on case (opens billing page instead of buying a second plan), and states authorization (owner or admin, billing:write scope). Also points to get_x_posting_quota for reading allowance.

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