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

With no annotations, the description carries the full burden. It discloses the monetary cost ($0.005), the payment mechanism (api_key or x402), and a behavioral caution about silent retirement of the value, suggesting follow-up actions. It does not detail the response format or error handling, but the cost and payment disclosure are significant behavioral traits.

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 concise relative to the information it conveys: cost, purpose, filtering, payment, and follow-up steps are all packed into three sentences. It is front-loaded with the paid flag and purpose. Each sentence earns its place, though it is dense and could be split for readability.

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 paid tool with no output schema and no annotations, the description covers the essential usage: cost, payment, date filtering, and post-call actions. It does not describe the exact response structure (fields like effective date ranges), but it gives a high-level picture. The absence of pagination or error handling is a minor gap, but overall it is complete enough for an agent to call 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% and each parameter already has a description. The description adds minor value by specifying the date format (YYYY-MM-DD) and clarifying the api_key's optional role and payment fallback, but it does not materially enhance the schema beyond that, so a baseline of 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 the tool returns 'Historical values of a reference series with effective date ranges', which is a specific verb+resource and distinct from siblings like get_snapshot or get_changes. It also mentions optional date filtering, leaving no ambiguity about what the tool does.

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 provides clear context: it is a paid operation, requires an api_key or payment via x402, and includes post-call guidance to bind get_changes or register_alert. It does not explicitly contrast with alternatives like get_series or get_snapshot, but the purpose and follow-up instructions give enough situational guidance.

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