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

With no annotations, the description carries the full behavioral burden. It usefully discloses two real constraints — data availability back to 1999 and that the date must be at least one day old — which are genuine behavioral traits. It says nothing about permissions, rate limits, or response shape, leaving the safety/operational profile incomplete.

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?

Two short sentences with no filler, and the primary purpose is front-loaded before the constraints. Efficient, though the second sentence could be tightened slightly.

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 4-parameter read tool with fully documented schema and no output schema, the definition covers purpose, data horizon, and the key input validation rule. Reasonably complete; a brief note on the returned structure or default base would close the remaining gap.

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 four parameters, including formats, defaults, and enums. The description only adds a constraint on `date` (past-day requirement, 1999 floor) and does not touch `type`, `currencies`, or `base_currency`; baseline 3 is appropriate given 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?

States a specific verb and resource ("Returns the exchange rates") with a scoping qualifier ("for a specific date") that implicitly separates it from getLatest and getRange. It never names a sibling explicitly, so the agent must infer the boundary, but the purpose itself is unambiguous.

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?

Usage is only implied by the scope phrase "for a specific date" and the constraint that the date must be in the past. No alternative is named (e.g., use getRange for multi-day spans, getLatest for today), and no exclusions are stated, so the agent gets context but no routing guidance.

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