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 cost ($0.005), payment flow via x402/api_key, and the response contents (source citation, effective date, last-confirmed date, staleness flag). It does not mention potential side effects, but as a read-only query that is implicitly safe. This is strong value beyond schema.

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 the cost flag front-loaded and no filler. Every sentence adds value: purpose, examples, response details, and payment instructions. It is optimally concise.

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 a rich overview for a simple 3-parameter tool: cost, payment, return data (including staleness). It omits the 'country' parameter from the prose, but the schema handles that. Given no output schema, the explanation of response fields is valuable and mostly 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?

Schema coverage is 100%, so descriptions already handle parameter meaning. The description adds examples for 'series' and clarifies 'api_key' behavior (bypasses x402, metered). It does not mention 'country', which is a slight gap, but the schema covers it. Overall, the description enhances parameter understanding.

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 'Current value of a reference series' with concrete examples (policy-rate, vat, minimum-wage), clearly distinguishing it from siblings like 'get_series_history' (historical) and 'list_series' (catalog). The verb+resource pattern is explicit and unambiguous.

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 clearly implies this tool is for retrieving current values, not historical or lists. However, it does not explicitly mention when not to use it or name alternative tools. The 'Current value' phrasing gives strong contextual guidance, but lacks explicit exclusion statements.

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