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

All annotations are false, so the description carries the full burden of behavioral disclosure. It adds genuinely useful behavior: one row per published day, summary statistics, and an over-wide window being shortened rather than refused. It does not explicitly state that this is read-only, but the description gives no hint of mutation either.

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?

Three tight sentences, each earning its place: purpose, output shape, and edge-case behavior. The most important information is front-loaded, and there is no filler.

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 6 parameters, no output schema, and no annotations, the description covers the core contract: what the tool returns, how it behaves on broad windows, and what data source it uses. It is slightly light on sibling differentiation and the exact meaning of 'change', but the rich input schema closes most remaining gaps.

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 the schema already documents all six parameters in detail. The description adds useful context about trailing windows and the free 90-day limit, but it does not provide parameter-level meaning beyond what the schema already covers. 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 states a specific verb-resource combination: 'ECB rate of one currency pair across a window.' It also names the exact return shape (daily rows plus min/max/avg/change), which clearly distinguishes it from siblings like rates_latest and rate_on. This is more than adequate for an agent to understand what the tool does.

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 opening line 'Call this tool for...' gives an implied usage context: historical rate queries with summary statistics. However, it never names alternatives or states when not to use this tool, so an agent must infer its position among siblings like rate_on and rates_latest.

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