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

Annotations only cover readOnlyHint and openWorldHint, yet the description discloses pricing ($0.01 USDC fixed per request), the payment rails (x402 on Base, MPP on Tempo), that 4xx errors are not charged, the licensing (CC BY 4.0), and the 20-country cap. That is exactly the kind of cost and failure-mode context an agent needs before invoking a paid endpoint.

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?

A single dense paragraph that front-loads the data shape before the commercial and licensing details. Nearly every clause carries information, though the payment-rail specifics (x402 on Base vs MPP on Tempo) run slightly long for a tool description.

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?

No output schema exists, so the description must convey the return shape, and 'annual values' over a year range for one indicator does that adequately. Cost, error-charging behavior, and key discovery are all covered; only per-row field structure is left implicit.

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, but the description adds value by supplying concrete indicator keys (inflation_cpi_pct, gdp_growth_pct, central_govt_debt_pct_gdp) and pointing to the key catalog. It does not clarify start/end defaults or the ISO3/ISO2 format beyond what the schema already says, so it stops short of a 5.

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 resource (World Development Indicator time series), the exact shape (one indicator, up to 20 countries, year range, annual values), and gives concrete indicator keys. It is not tautological and the scope implicitly separates it from macro_rank and macro_country, though it never names those siblings 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?

Provides a real prerequisite — 'See free /macro/indicators for keys' — which tells the agent how to obtain a valid indicator value before calling. However there is no explicit when-to-use-this-vs-alternative guidance against macro_country, macro_rank, or rates_timeseries, so selection is left to inference.

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