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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds value by revealing the data source ('Source: European Central Bank'), which is not present in annotations or schema. This provides context on data origin and reliability. It does not contradict annotations. However, it does not describe return structure or rate-limiting behavior, but given the output schema exists, that is acceptable.

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 exactly two sentences: one for core functionality and one for data source. Every sentence adds distinct value with zero filler or redundancy. It is highly efficient and front-loaded, making it easy for an agent to parse quickly.

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?

For a simple tool with only two enum parameters, rich annotations (read-only, idempotent), and an output schema, the description is fairly complete. It states what is returned (historical daily rates), the scope (G10 pairs), and the source (ECB). However, it does not explicitly mention that it returns a time series, nor does it provide any usage context like typical applications. Given the low complexity, a score of 4 is appropriate; it is not fully maximized.

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?

The input schema provides 100% coverage of both parameters, including enums (currency pairs and time windows) and per-parameter descriptions (e.g., days: '30 ($0.05)'). The tool description adds no additional parameter-level meaning beyond what the schema already contains. Baseline 3 is appropriate because the schema does the heavy lifting; the description adds no extra semantics.

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 uses a specific verb ('Returns') and resource ('historical daily exchange rates for a G10 currency pair'), which clearly states the tool's function. It is distinguishable from siblings like 'get_fx_rate_current' (current rates) and 'get_fx_rate_by_date' (single-date rates) due to 'historical daily' implying a time series, though it does not explicitly name alternatives. The title 'Get G10 FX Rate History' reinforces the purpose. A score of 4 reflects clear purpose without explicit sibling differentiation.

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 provides no guidance on when to use this tool versus alternatives. It does not mention exclusions or when to prefer other FX tools such as 'get_fx_rate_current' or 'get_fx_rate_by_date'. There is also no mention of use cases or limitations. This is a clear gap in usage guidance.

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