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

With no annotations supplied, the description carries the full load and does well: it discloses the paid access model ($0.002 USDC/call via x402 on eip155:8453), the upstream source (ECB fixing), the peg fallback path, and that the response carries rate date, method and source attribution. What it omits is operational behavior an agent would want — staleness/freshness windows, holiday or non-publishing-day handling, and failure modes when a fixing is unavailable.

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?

Dense but front-loaded: the payment/transport tag comes first, then the resource, then the qualifying conditions. Every clause contributes something (cost, source, peg handling, output fields, determinism), though the single run-on sentence makes scanning slightly harder than a short bulleted form would.

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-param lookup with no output schema, the description covers what an agent needs to call it and to trust the result: the pair, the source, the fallback rule, the method taxonomy and the attribution fields. The remaining gaps are freshness semantics and what a caller gets on days with no ECB publication.

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 no parameters and the description makes clear why: the pair and the source are fixed by the tool itself. Baseline 4 applies for a zero-parameter tool, and nothing in the description implies hidden inputs such as a date argument.

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 and pair ('Official OMR/USD reference rate') plus the exact provenance (latest ECB fixing, or the official peg when USD is pegged). This is instantly distinguishable from siblings like fx_omr_eur, fx_usd_omr, fx_latest, fx_convert and fx_timeseries, which cover other pairs or other operations.

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 implied by the fixed pair in the name and by 'reference rate', but the description never says when to prefer it over fx_convert (for arithmetic), fx_timeseries (for history) or fx_latest (for multiple pairs), nor does it state exclusions such as 'not a live intraday quote'. Routing is inferable rather than instructed.

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