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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description's main job is to add non-obvious traits — and it does: a $0.01 USDC payment on Base via x402, CC BY 4.0 licensing, annual granularity, and a hard 20-country cap. Return structure (field names, missing-data handling) is not disclosed, but the paid-call constraint is the critical operational fact and it is front-and-center.

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 sentence front-loads what is returned, then the key-discovery pointer, then license and cost. No filler; the metadata about payment and licensing each carry operational weight.

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 4-parameter read-only fetch with full schema coverage and no output schema, the description covers scope, granularity, limits, discovery of keys, and the payment model. Only the shape of returned data and behavior on sparse/missing country-year values is left unstated, which is a minor gap.

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 all four parameters are already documented in the schema, including defaults and the ISO3/ISO2 max-20 constraint. The description reinforces the indicator examples and country cap but adds essentially no semantics beyond the schema text; baseline 3 applies.

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-resource pair: fetch one World Development Indicator across up to 20 countries over a year range, with annual values. The explicit 'one indicator' scope cleanly separates it from macro_rank (ranking) and macro_country (country profile) without needing to name them.

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?

Prerequisite to obtain a valid indicator key is given ('See free /macro/indicators for keys'), which implies the usage flow. However, there is no explicit guidance on when to pick this tool over macro_country, macro_rank, or the rates_* siblings, so the agent must infer the boundary from scope alone.

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