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

Annotations declare non-read-only, non-idempotent, non-destructive, but the description adds genuinely non-obvious semantics: the call cannot charge the human, payment is explicit and human-driven, and an existing checkout is reused rather than recreated. That materially changes how an agent should treat the result, though it says nothing about expiration of the returned URL or auth requirements.

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, front-loaded with the return value, then behavior. Every sentence earns its place with no filler. Slightly clipped phrasing ('existing subscribers receive account management') costs it the top mark.

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?

With only one optional enum parameter, a full schema, an output schema, and annotations present, the description carries what it needs to: what is returned and the non-charging, human-driven nature of the flow. The gap is routing among billing/checkout siblings, which an agent must guess.

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% and the single enum parameter is fully documented, so the baseline is 3. The description's 'omit to reuse an existing checkout' merely restates what the schema already says about the optional plan parameter, adding no new meaning.

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 — 'Return the org-bound checkout URL' — so the agent knows this yields a URL for a checkout flow. It is distinguishable from siblings like get_billing_status and get_mac_checkout by the 'org-bound' and plan-purchase framing, though it never names which sibling to prefer.

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?

Usage is implied rather than stated: the description explains that a human picks a plan and pays, and that existing subscribers get account management, which hints at the right scenario. But it never explicitly says when to call this instead of get_billing_status or get_mac_checkout, and gives no prerequisites.

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