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

With no annotations, the description carries the full burden; it does disclose the access-tier requirement ('Pro and Enterprise keys'), which is valuable and non-obvious. It omits freshness/update cadence, whether the call is read-only (inferable from the name), and any rate limits or failure modes.

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, front-loaded with the metric definition, with zero filler. It reads as a sentence fragment and could open with a verb for clarity, but nothing is wasted.

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?

The output schema exists, so enumerating return fields is redundant though harmless, and the key tier info is a genuine addition. However, a low-complexity lookup tool still lacks any usage context or coverage notes (which currencies are supported), leaving it only minimally 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 coverage is 100%, with both currency (ISO 4217, examples EGP/NGN/ARS) and lang fully documented in-schema. The description adds nothing beyond that, so the baseline 3 applies.

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 defines the specific metric computed (street rate vs. official central-bank rate) and enumerates the resulting fields, which implicitly separates it from get_street_rate (street only). It never states a verb like 'get' or 'compute', so the purpose is clear but slightly implied rather than asserted.

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?

There is no guidance on when to use this versus get_street_rate, get_rate_history, or get_stress_signals, all of which overlap on FX data. The only routing signal is the implicit 'this one includes the official rate'.

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