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

With no annotations supplied, the description carries the full burden and does well: it discloses the paid cost ($0.002 USDC/call), the payment protocol and chain (x402, eip155:8453), the upstream data source, the fallback rule when ILS is pegged, and that values are deterministic with no estimation. It stops short of stating refresh cadence beyond 'latest ECB fixing', failure modes, or rate limits.

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 with the cost/payment bracket front-loaded before the purpose, and no redundant clauses. Minor friction from raw protocol notation like 'eip155:8453' being given without the human-readable chain name.

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 quote tool with no output schema, the description covers the essentials: what is returned (rate, date, method, source), how the rate is derived, and what it costs to call. Only staleness/cadence and error behaviour remain unstated, which are minor for this shape of 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?

The tool takes zero parameters, so the baseline is 4 and there is nothing for the description to compensate for. The currency pair is fully encoded in the tool name, leaving no ambiguity about what is being quoted.

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 names the exact resource (CAD/ILS reference rate) and the issuer of that rate (European Central Bank fixing, or the official peg when applicable), so an agent can tell it apart from the inverse fx_ils_cad or the cross-pair tools without opening the schema. It goes further by listing what the payload reports: rate date, derivation method, and source attribution.

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 when-to-use guidance at all — nothing says to prefer fx_convert for converting an amount, fx_timeseries for historical series, or fx_latest for a broad snapshot. In a catalogue of hundreds of fx_* siblings, that routing information is the main thing an agent needs and it is absent.

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