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

The description discloses a key behavioral trait: using the tool requires a payment of $0.01 USDC Base x402. It also sets expectations about the non-authoritative nature of the data ('Not a tax ruling'). However, it does not specify whether the tool is read-only, whether the payment is a one-time fee or per-call, or what the exact return format looks like.

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 brief and to the point. Each sentence serves a purpose: listing the rates, clarifying the indicative nature, and flagging the payment. There is no redundant or filler content, making it highly efficient for an agent to parse.

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?

The description provides core information about the data and the cost, but lacks some context. It does not specify the output format (e.g., a table, a JSON object), how the payment is processed or verified, or any special instructions for invoking the tool. Given the low complexity, these omissions prevent it from being fully complete.

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 schema is an empty object with additionalProperties true, meaning any parameter could be passed but no parameters are formally defined. The description does not clarify what inputs (if any) the tool accepts, such as a product category or a year. This leaves the agent with no guidance on how to pass parameters or whether parameters are even allowed.

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 identifies the tool as an indicative French VAT rate table with the exact rates listed (standard 20, intermediate 10, reduced 5.5, super_reduced 2.1, exempt). It unambiguously states what resource is being provided and distinguishes it from tax advice by saying 'Not a tax ruling.' This makes the purpose immediately clear.

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 gives no explicit guidance on when to use this tool versus alternatives. While it notes the table is 'indicative' and 'Not a tax ruling,' it does not mention any sibling tools or conditions for selection. An agent would not know whether to pick this over related tools like 'vat_key' or 'ht_ttc' based on the description alone.

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