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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), so the bar is lower. The description adds genuine context beyond them: the rate is 'official' and 'daily', and the quote direction is fixed as 1 EUR = X, which prevents an agent from misreading the inversion. It does not mention weekend/holiday gaps or behavior for an unsupported currency.

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 sentence with zero waste; the scope ('official daily ECB euro reference rate'), the direction ('1 EUR = X'), and the input ('ISO 4217 code') are all front-loaded.

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 one-parameter tool with no output schema, the description effectively describes the return value ('1 EUR = X currency'), which is what an agent most needs. It stops short of covering error cases (unknown/unsupported currency) and whether a reference date is returned.

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 coverage is 100%, so the schema already documents the currency parameter including the ISO 4217 constraint and examples. The description only repeats the same examples (USD, GBP, CHF) without adding format, casing, or error semantics.

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 verb (Return), resource (official daily ECB euro reference rate), and the exact output format (1 EUR = X currency) so the agent knows precisely what it gets. It is unmistakable against siblings like eurlex_lookup, vies_validate, or legal_lookup, none of which deal with FX rates.

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 description — an agent can infer it is the tool to call for a EUR exchange rate — but there is no explicit when-to-use, no exclusions, and no alternative tool named. Minimum viable guidance.

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