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

Annotations already declare read-only and idempotent, and the description adds substantial behavior beyond them: hard caps per frequency (30 annual, 40 quarterly, 120 monthly, 52 weekly, 250 daily), the truncation flag, projection labeling with a separate next_projection field, and the returned metadata (unit, source, licence, period range, chart link). That is exactly the kind of operational 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 the core behavior and frequency caps, then the mode selection, then return contents. It is dense but long; the parenthetical repetition of the year-coverage math ('about 30 years of annual data...') slightly duplicates the cap list already given.

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 carries the return-shape burden and does so by naming the included fields (unit, source, licence, period range, chart link) and the next_projection field. An agent has enough to call it and interpret the result without further inference.

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 baseline is 3, and the description genuinely adds meaning: it explains the interaction between year and start_year/end_year, that year returns the last period of that year for monthly or quarterly data, and that country is an ISO 3166-1 alpha-3 code. It stops short of explaining the indicator slug format, which the schema already covers.

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?

Opens with a specific verb and resource ('Returns values of one indicator for one country or region') and states scope precisely enough to separate it from get_indicator_details or search_indicators. It does not explicitly name the sibling tools, so the differentiation must be inferred from the resource noun rather than stated.

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?

Gives clear conditional guidance for the three calling modes: no years = latest values, start/end_year = a range, year = a single value. That is strong within-tool routing, but it offers no explicit statement about when to prefer compare_countries or get_indicator_details instead.

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