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

With no annotations, the description carries the full burden for behavioral disclosure. It reveals return shape (dated series plus summary figures), the fixed base date, starting value, and the heavy result warning for daily resolution. However, it omits details like auto-thinning (mentioned in schema) and any potential error behavior, so it is good but not exhaustive.

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?

The description is three sentences: purpose, output summary, and resolution guidance. It is front-loaded with the core action and key historical anchor, with no fluff or redundant phrasing.

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?

Given the tool has no output schema and no annotations, the description adequately conveys what results to expect (dated series + summary figures) and provides the necessary context for typical usage. It is not overly complex, but it lacks edge-case details (e.g., invalid date ranges, exact handling of thinning) which prevents a 5.

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% with all parameters already described in the input schema. The description mainly repeats the default date and resolution behavior (start date 2017-01-10, monthly default) without adding new parameter-specific nuance. Baseline 3 is appropriate since the schema does the heavy lifting.

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 states a specific verb+resource+scope: "Get the historical value of the ieUnit in USD since its fixed base date 2017-01-10." It clearly distinguishes from siblings by saying "Use this for questions about how the ieUnit developed over time," which differentiates it from value/convert/compare tools.

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?

The description gives explicit usage context ("Use this for questions about how the ieUnit developed over time") and explains resolution trade-offs ("Defaults to monthly resolution; daily data is available but produces large results over long ranges"). It does not explicitly name alternative tools or state when not to use it, so it falls short of a 5.

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