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

With no annotations, the description carries the full burden and does so well: it discloses the payment model and network, the upstream authority (ECB), the derivation method (direct, cross via EUR, or peg-derived), and that values are deterministic and never estimated. It does not cover update cadence/latency (when a new fixing becomes visible) or failure behavior when no fixing exists, which are the remaining gaps for a paid data call.

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?

Two sentences, front-loaded with the pricing/transport tag before the substantive purpose, and every clause (source, date, method, attribution, no-estimate) adds a distinct fact. Slightly dense in the second half, but nothing is redundant.

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 zero-parameter, no-output-schema tool the description covers the important parts: what rate, from where, with what derivation, and what metadata accompanies it. What remains unstated is the orientation of the quoted rate and how stale the 'latest' fixing can be, both of which an agent consuming the number would want.

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?

The tool takes zero parameters, so there is no schema meaning to add; the description correctly spends its words on what the fixed invocation returns instead of inventing parameter guidance. Baseline 4 applies, with no gap introduced by the empty input schema.

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 (CHF/MYR reference rate) plus the data source (ECB fixing) and the fallback case (official peg when MYR is pegged), which is far more than the bare pair name. Against hundreds of fx_* siblings it establishes the pair and the authoritative source, but never states the quote orientation (MYR per CHF vs CHF per MYR), leaving the direction to be inferred from naming convention rather than from the text.

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 makes the decision-relevant cost explicit ($0.002 USDC/call via x402 on eip155:8453), which helps an agent decide whether to call at all. However, it names no alternative: siblings like fx_convert, fx_latest, fx_timeseries, or the inverse pair fx_myr_chf are never mentioned, so when-to-use versus other FX routes is only implied by the pair in the name.

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