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

Annotations already declare this as a safe, read-only, idempotent, closed-world operation, and the description adds genuinely non-redundant behavior: zero credit cost, keyless operation, per-IP rate limiting on keyless calls, and the important semantic that a date with no exact fixing resolves to the latest fixing on or before it. Values are explicitly unchanged from the BNR source, which tells the agent how much to trust the output.

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?

Front-loaded with the resource and modes, then cost/auth, then provenance — a sensible priority order with no filler. The first sentence is densely packed with nested parentheticals, which costs a bit of readability, but each clause carries real information.

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 no output schema, the description still conveys what comes back (all currencies or one for a date; a daily series over a range) and notes values are verbatim from BNR. Missing only the response field shape and pagination/format details, which are minor for a two-mode lookup tool.

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 only 50% — `from` and `to` have patterns but no descriptions — and the description compensates by explaining that they define a daily series bounded at 366 days, plus that currency defaults to EUR for history and is optional for single-date (all currencies vs one). It does not clarify whether `currency` is mandatory for the series mode, leaving the from/to+currency interaction slightly underspecified.

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 resource (BNR reference exchange rates in RON) and immediately enumerates its two operating modes: single-date fixing lookup and daily series for one currency. The scope (from 2005-01-03) and the source (bnr.ro) make it unmistakably distinct from the sibling tools, none of which deal with FX rates.

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 effectively routes the caller: use `date` for a single fixing (latest on/before that date, all currencies or one) or `from`/`to` for a daily series in one currency, capped at 366 days. It gives clear conditions for each mode but names no alternative tool or exclusion, so it stops short of full when/when-not guidance.

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