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

With no annotations, the description must carry the full behavioral burden. It explains the calculation formula (days / days in start month) and includes a cost note ('Paid $0.01 USDC Base x402'), which hints at a monetary side effect. However, it does not disclose whether the operation is read-only, what happens with invalid dates, rounding behavior, or any error conditions. The cost note is positive but incomplete.

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 two sentences with no fluff. The core purpose is front-loaded, and the cost note is secondary. It is concise and structured logically, though the pricing information could be separated for clarity.

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 tool with no output schema and no annotations, the description is too sparse. It does not specify the return value (the calculated prorated amount), the expected input format (e.g., date strings, numeric amount), or edge-case behavior. An agent would struggle to call this tool correctly without further information.

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 defines zero parameters (additionalProperties: true), so the description must compensate. It references 'monthly HT amount' and 'from/to window,' implying the expected inputs, but does not provide parameter names, types, or required flags. Baseline for 0 params is 4, but the description's ambiguity about exact argument structure lowers it to 3.

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 states a specific calculation: 'Calendar prorata of a monthly HT amount over an inclusive from/to window.' It identifies the verb (prorata), resource (monthly HT amount), and window (inclusive from/to), but leaves inputs vague—no mention of how the amount or dates are provided. It distinguishes from siblings by being a calculation tool, though not explicitly.

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?

There is no guidance on when to use this tool versus alternatives. The sibling list includes related terms like 'jours_francs' (days) and 'ht_ttc' (tax conversions), but the description does not explain when prorata is appropriate or which sibling to choose instead. No when/when-not guidance is given.

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