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

Annotations indicate a non-read-only, non-destructive, non-idempotent operation. The description adds that no charge occurs until payment, that a purchase_token is returned, and that one payment unlocks all formats. It also discloses licensing terms. It does not mention other side effects (e.g., token expiration), but the added context goes beyond the annotations.

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 four sentences but packs in price, payment flow, follow-up steps, format details, account alternative, and licensing. No filler words; every sentence serves a distinct purpose.

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?

This tool is part of a multi-step purchase process, and the description fully covers the end-to-end flow: quoting, payment integration, download retrieval, and format coverage. It also mentions licensing and the free-account alternative. There is no output schema, so the description's mention of the purchase_token fulfills the need to explain return behavior.

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 input schema already documents both parameters at 100% coverage, including detailed engine descriptions and model_id provenance. The description adds engine-specific format outcomes, but that is more about results than parameter semantics. Since schema covers parameter meaning, 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 begins with 'Quote an anonymous purchase of a library model,' using a specific verb ('Quote') and resource ('library model'). It includes the price point (1.50 CHF flat) and the return of a purchase_token, which clearly differentiates this tool from siblings like pay_training_job or create_commercial_license.

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 explicitly maps the workflow: use buy_library_model to get a token, then pay with pay_training_job, then fetch with get_library_purchase. It also provides exclusions and alternatives: the model is free with an account on the website, and commercial licensing is a separate paid product. This gives the agent clear when-to-use and when-not-to-use guidance.

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