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

Beyond the readOnly/destructive annotations it discloses latency ('every call answers at once'), data provenance and vintage (committed World Bank snapshot, CC BY 4.0, snapshot date in the answer), pricing per call, that failed calls are free, and that repeats are not free — which explains the idempotentHint=false flag. That is substantial behavioral context annotations cannot carry.

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-loaded with purpose, fields and country input before secondary detail; every sentence communicates something. The billing point is stated twice ('Price $0.01/call... failed calls free' and 'each call is charged, so repeats are not free'), which is mild redundancy.

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?

With no output schema, the description still names the returned measures, their units, the year ordering and count, and notes the snapshot date is included in the answer. Combined with the disclosed cost model, an agent has everything needed to call it and interpret the result.

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 still adds ordering information not present in the schema ('last 1-10 years with the newest year first') and restates accepted country identifiers with an example. It does not clarify what happens for out-of-range or unknown-country inputs.

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 opens with a specific verb and resource ('Population of any country from World Bank data') and enumerates the three returned measures. It is clearly distinguishable from siblings such as econ_gdp, econ_inflation and econ_unemployment by resource, so an agent can pick it without inspecting schemas.

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?

It gives concrete usage context ('Use for market sizing, per-capita figures and demographics') and an example call (country=SE). It never names an alternative tool or states when not to use this one, so guidance is clear but not exclusionary.

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