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

With no annotations, the description carries the full burden, and it does well: it discloses the output shape (unit, per-country series of {year, value, forecast_flag}, plus a top-level forecast_flag) and defines the non-obvious forecast rule ('a point is a forecast when year >= the current UTC year'). It does not mention error behavior, missing-year handling, or rate limits, but the core behavioral traits are covered.

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?

Two tightly written sentences: the first states purpose and scope, the second delivers output structure and the forecast rule. Nothing is wasted and the most decision-relevant information (what it returns, scope) is front-loaded.

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?

There is no output schema, so the description must explain return values — and it does, giving the output shape, the unit field, and the forecast_flag semantics with an explicit rule. Combined with a complete input schema, an agent has everything needed to call and interpret this tool.

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%, so all four parameters are already documented, including the comma-separated country-code format, the 20-country cap, and the year bounds. The description only restates that the year range is optional and gives an indicator example, adding little beyond the schema — baseline 3 is appropriate.

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 names a specific verb ('Returns'), a specific resource ('one IMF DataMapper indicator'), the example indicator NGDP_RPCH, and the scope ('one or more countries, optionally limited to a year range'). It is unambiguously distinguishable from the sibling search_indicators, which is a lookup tool rather than a data-fetch tool.

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?

Usage is implied through the example indicator and the scope statement, but the description never states when to prefer this tool over search_indicators (the guidance 'Find codes with search_indicators' lives in the schema, not the description), nor any prerequisites or exclusions. An agent can infer the pairing, but it is not stated.

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