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

With no annotations, the description carries the full burden, and it does disclose useful non-schema facts: the data source (ECB reference data) and a cost of 1 credit. It does not say what the response contains, whether rates are ECB-daily (so non-business days may fall back), or what errors look like for bad dates/currencies.

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?

A single sentence that front-loads the resource and source, then the supported knobs, with the cost tucked into a short parenthetical. Nothing is wasted, though the parenthetical credit note slightly interrupts the parameter list.

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, zero-required, no-output-schema tool with no annotations, the description covers source, scope and cost but omits the return shape and edge-case behavior — both of which the agent must guess absent an output schema. Adequate but not complete.

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 baseline is 3; the description only restates that base, symbols and amount are optional and that any base works. It leaves the effect of 'amount' unexplained — whether it returns a converted value or a rate table — which is the one piece of meaning the schema does not convey.

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 names a specific resource (ECB reference exchange rates) and enumerates the supported variations: latest or a given date, any base, optional symbols and amount. It is unambiguous and clearly distinct from the time/holiday siblings, though it never explicitly contrasts itself with them (the domains differ enough that this is minor).

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 implied by 'latest or a date' and by calling out which fields are optional, so an agent can infer the normal call pattern. There is no explicit guidance on when to prefer this over another tool, what happens with an invalid date or unsupported symbol, or any prerequisite, so it stays at minimum-viable.

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