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

Annotations already indicate read-only, idempotent, non-destructive, and closed-world behavior, but the description adds substantial operational context: it never charges, cannot complete or confirm payment, must never ask for card details, and returns the pricing page without an API key. These details go well beyond the structured annotations and are exactly what an agent needs to avoid misusing the tool.

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 most important constraint ('Does NOT charge anything') and then efficiently covers the return value, the user's payment flow, the payment-confirmation boundary, and the no-API-key fallback. Every sentence earns its place, and there is no redundant or filler text.

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?

Given two simple parameters, no output schema, and rich annotations, the description supplies the missing behavioral and return-context information an agent needs. It explains what the link is, what the user does with it, what the tool cannot do, and what happens without an API key. Nothing essential is missing 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?

Schema description coverage is 100%, and both parameters are already documented in the schema: plan as the id or exact name from list_plans, and promo_code as an optional user-provided code. The description mentions the chosen Pro plan and optional promo code but adds no format, source, or validation detail beyond the schema, so the baseline 3 is appropriate.

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 clearly states a specific action and resource: it returns a personal checkout link for the chosen FirmLedger Pro plan, optionally with a promo code. It also draws a sharp boundary by saying it does NOT charge anything. However, it does not explicitly differentiate this tool from sibling prepare_* tools, so it falls short of a 5.

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?

It gives clear contextual guidance: give the user the link so they can sign in and pay on Lemon Squeezy themselves, and if the user says 'yes, do it,' give the link again. It also states the no-API-key fallback of returning the pricing page. It does not name an alternative sibling tool or state when not to use this tool beyond the payment-boundary context.

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