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

With no annotations, the description carries the full burden and does meaningful work: it discloses data provenance (ECB and BAM fixings), that crosses may be computed rather than direct, and that each call costs $0.003 USDC via x402 on Base. It stops short of stating rate limits, error/refund behavior, or whether the fee applies to failed calls.

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 dense sentence front-loads the resource and scope, then tacks on computation and payment details. Everything earns its place, though the pricing clause shares a sentence with currency scope rather than being separated for scanability.

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 2-parameter, non-nested tool with no output schema, the description covers source, coverage, computation method, and cost. The one gap is return shape: it mentions 'method and date' in passing but does not tell the agent what fields come back for a multi-quote request.

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% (base and quote are documented, including the comma-separated multi-quote form), so baseline is 3. The description adds only the indirect hint that quote accepts multiple currencies via 'any pair' framing, which is weaker than the schema's own wording.

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?

Names a specific resource (official ECB and Bank Al-Maghrib reference exchange rates) and a precise scope (~50 currencies, named EM/MENA examples, direct or computed crosses). It never states a verb or distinguishes itself from the nearby sibling macro_policy_rates, so an agent must infer the boundary itself.

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 domain: an agent can deduce 'use this for FX conversion' but the description never says when to prefer it over macro_policy_rates or how to handle unsupported currency pairs. No exclusions or alternatives are given.

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