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

With no annotations supplied, the description carries the full behavioral burden and adds substantial context: it names the ECB as the source, describes fallback behavior (official peg when ILS is pegged), and discloses the derivation method (direct, cross via EUR, or peg-derived). It also states the tool is deterministic, sourced with no estimation, and priced at $0.002 USDC per call via x402. It does not mention rate limits, caching, or update frequency beyond "latest."

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?

The description is a single dense sentence with the resource and source front-loaded, followed by the relevant behavioral details. Every clause adds information about source, fallback, method, or cost, with no filler.

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?

Since no output schema exists, the description must describe the return shape, and it does so reasonably: rate value, rate date, derivation method, and source attribution. For a parameterless lookup tool with no annotations, this is nearly complete, though it does not name exact response fields or units.

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 parameter semantics for the description to explain and the baseline is 4. The description correctly presents the call as parameterless and self-contained.

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 states a specific verb and resource: it returns the official EUR/ILS reference rate from the ECB fixing, including the rate date and derivation method. It identifies the exact currency pair clearly, though it does not explicitly distinguish itself from siblings like fx_eur_ils inverse fx_ils_eur or the generic fx_convert.

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 explains what the tool returns but gives no explicit guidance on when to use it versus alternatives such as fx_convert or fx_ils_eur. Usage is only implied by the pair-specific name, so an agent must infer selection from the tool name rather than the description.

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