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

Annotations cover safety (readOnly, idempotent), but the description adds critical context beyond them: it is paid ($0.01), requires a payment mechanism (api_key or x402), explains what happens without a key, and describes the returned payload's fields (value, unit, effective and last-confirmed dates, official source, confidence label). It also warns about downstream binding to get_changes or register_alert. This is rich behavioral context that annotations cannot convey.

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 front-loaded with the price and the core purpose, then moves to payment mechanics and follow-up recommendations. Every sentence carries information, though the final sentence about binding get_changes/register_alert is somewhat tangential to the brief itself and could be moved to a 'see also' note. Still, no filler.

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?

Given the tool is paid and has an output schema, the description covers pricing, authentication, payment fallback, and the richness of the returned data. It also covers a post-success workflow. Nothing essential for an agent to invoke it correctly is missing.

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 the baseline is 3. The description adds meaning beyond the schema for api_key by explaining its purpose (payment) and the fallback payment flow via x402. The country parameter's enum is already in the schema, so no extra credit there. It also implicitly sets expectations about the response shape when no key is passed.

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 specific verb (brief) and resource (country), enumerates the exact series returned (policy rate, VAT/GST, CPI, taxes, minimum wage, holidays), and distinguishes itself from siblings that fetch single series (get_series, get_series_history). An agent knows precisely what this tool yields without opening the 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?

Explains when to use it (one call for every reference series for a country) and why it is preferable to buying series one by one. It also names follow-up tools (get_changes, register_alert) and the condition for using them. It does not explicitly say when NOT to use it (e.g., when only one series is needed, use get_series), but the comparative hint is strong.

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