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

Annotations already cover readOnly/idempotent/openWorld/non-destructive, so the description earns credit for adding the non-obvious commercial and auth behavior: $0.01 cost, two payment paths (api_key or x402), and the post-call binding recommendation. It omits error/rate-limit behavior, and the register_alert pricing line reads as cross-sell rather than behavior of this tool.

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?

Front-loads purpose and value in the first sentence, then cost/auth, then follow-up — a sensible order with little waste. The trailing register_alert pricing parenthetical adds length that serves the vendor's upsell more than the caller's decision, slightly diluting an otherwise tight paragraph.

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?

Covers what the payload contains (value, unit, effective and last-confirmed dates, official source, confidence label), the cost, the auth paths, and the recommended next step. With an output schema present the return shape need not be restated, so the only real omission is failure-mode behavior (e.g., what happens without payment or for an unsupported country code).

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 description coverage is 100% and the country enum is self-documenting, so the baseline is 3. The description goes slightly beyond by explaining the role of api_key ('if you have one; card checkout at /pricing') and the fallback payment flow, which the schema's bare 'API key' label does not convey.

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?

States a concrete verb+resource ('Country brief: every reference series we hold for one country') and enumerates the content types (policy rate, VAT/GST, CPI, taxes, minimum wage, holidays). This clearly separates it from single-series siblings like get_series/get_series_history, so an agent can pick it without opening any schema.

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?

Gives clear context ('Cheaper than buying the series one by one') that positions it against per-series calls, plus the auth prerequisite ('Pass api_key if you have one... otherwise the response explains how to pay via x402'). It also prescribes a follow-up ('bind get_changes or register_alert'). It stops short of an explicit when-not or a named alternative tool, so not a 5.

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