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

With zero annotations provided, the description carries the full disclosure burden, and it does substantial work: it reveals the payment prerequisite (PAYMENT-SIGNATURE via x402 v2), discloses the return value (Bearer JWT), and explains the price/quota consequence of each plan choice. It does not mention idempotency or double-charge risk for a money-moving operation, which would be valuable, but it goes well beyond a minimal statement.

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?

Two dense sentences with zero filler. The core purpose is front-loaded, followed by the plan pricing table, then the authentication requirement, then the return type. Every clause earns its place and carries decision-relevant or call-relevant information.

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 1-optional-param tool with no output schema and no annotations, the description covers the essentials: purpose, plan options with cost implications, the required payment signature, and the Bearer JWT response. Minor gaps remain around renewal mechanics (extends vs. replaces an existing subscription) and failure behavior, but nothing that blocks a competent agent from invoking 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% — the schema documents plan as an enum with 'SKU to purchase. Default agent.' The description adds real decision-making value beyond the schema by attaching price and quota semantics to each enum value (15 USDC/20 sheets, 79 USDC/200, 250 USDC/fair-use), which an agent needs to select the correct plan.

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 the specific verb+resource pair 'Subscribe or renew,' which is a clear statement of the tool's function. The plan options and pricing further define the action, and the tool is immediately distinguishable from all siblings, which are fiche-management operations (create_fiche, delete_fiche, share_fiche, etc.).

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 context is implied rather than stated: the tool is for purchasing or renewing a subscription, and the siblings are all fiche operations so there is no real overlap. However, the description never explicitly says 'use this when ...' or mentions exclusions such as when a renewal should be skipped or when a different sibling would be appropriate.

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