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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely useful context beyond that: the rate is the one inv.bg applies to documents, plus the underlying GET endpoint. It says nothing about behaviour for non-business days or unsupported currency codes.

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 front-loaded sentence carrying the direction of conversion, the date scope and the document context, plus a short endpoint reference. Nothing is padded, though the raw path adds little for an agent that already has the tool name.

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 two-parameter read with full schema coverage and no output schema, most of what's needed is present. It still leaves open what the response contains (a single numeric rate), how non-trading days resolve, and how an invalid currency code is reported.

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% and both parameters are documented there, so the baseline is 3. The description does add meaning by fixing BGN as the quote currency and the default date, but repeats the schema's 'default: today' rather than extending it (no format or validation detail beyond the pattern).

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+resource (exchange rate of a currency to BGN) plus scope (a date, default today), which distinguishes it cleanly from the CRUD siblings. No explicit sibling differentiation is needed since no other tool touches currency rates, but the description never names that contrast.

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?

'as inv.bg uses it for documents' implies the intended use case — matching the rate inv.bg itself applies — which is a real hint about when to prefer this over an external FX source. However, there is no explicit when/when-not statement and no alternatives or prerequisites (e.g. what to do for non-BGN targets).

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