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

With no annotations, the description carries the full burden and does well: it discloses the upstream source (ECB via frankfurter.dev), the refresh cadence (every business day), the one-hour cache TTL, and a per-call price with chain/currency. It omits error/rate-limit behavior and what an empty 'from'/'to' means, but the operational profile is substantially richer than the schema alone.

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?

Front-loaded and compact — the data source and the two modes come first, with pricing appended. No wasted framing, though the em-dash price block is somewhat dense.

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 5-parameter, no-annotation, no-output-schema tool, the description covers provenance, freshness, and cost but leaves the op-to-parameter mapping and response shape unexplained. The agent has enough to know what it is, but not fully how to fill all five required fields correctly per mode.

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 baseline is 3, and the schema descriptions are notably terse ('Operation', 'Convert to', 'Amount'). The description mentions the base-currency table and amount conversion but never clarifies which of the five required parameters apply to which op, leaving that inference to the agent.

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?

Names a specific verb/resource ('Live foreign-exchange reference rates from the European Central Bank') and enumerates the two operating modes (full rate table vs cross-rate conversion). This clearly differentiates it from sibling tools like crypto_price, converters_*, and finance_* calculators.

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 describes the two available behaviors but never explicitly maps them to the 'rates'/'convert' op values, nor states when to prefer this tool over alternatives such as crypto_price or the static converters. Usage is implied rather than directed.

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