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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond that: an API key unlocks full history while keyless access is capped at the last year, cut periods are flagged depth_limited, status=empty signals no values, and it clarifies this is a platform estimate rather than exchange data. These are exactly the behavioral traits annotations cannot express.

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-loads the core purpose in the first sentence, then layers usage, key/coverage behavior, output field meanings, and failure status. It is dense and multi-topic, but every sentence carries decision-relevant information; slightly crammed rather than padded.

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?

An output schema exists, so return values need not be enumerated, yet the description still explains the notable fields (as_of, as_of_oldest, status=empty, depth_limited) and the key-based coverage limit. For a read-only historical series tool, this is complete enough to call correctly.

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 schema already documents all three parameters including the YYYY-MM-DD formats. The description restates the date format but adds no syntax or constraint beyond the schema, so the baseline 3 applies. Its extra semantics (as_of, depth_limited) describe output, not parameters.

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 (serve a daily series) and resource (ONE indicator) with explicit scope (over a period) and names what it returns (date, value 0–100, zone, methodology version). It also differentiates itself by naming siblings get_indicator and list_indicators as the wrong choices for a single point-in-time value.

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 explicit when-to-use ('how has the index changed since…' and for a chart), when-not-to-use (when only the current value is needed, routing to get_indicator or list_indicators), and the parameter format (date_from/date_to as YYYY-MM-DD). Nothing 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.