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, an explicit per-call price ($0.001 USDC via x402 — a payment/auth prerequisite the agent must know), and a sample response payload. It omits failure modes and any rate-limit or fallback behavior, which keeps it below 5.

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 with the resource and purpose, then source, pricing and output example — each sentence earns its place. The example output is verbose but substitutes for a missing output schema, so it is justified rather than padding.

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 3-param, zero-required read tool with no annotations and no output schema, the description supplies source, cost, use cases and a concrete response shape. Remaining gaps — default base currency behavior when omitted and error handling — are minor for this complexity.

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 base, date (YYYY-MM-DD) and symbols (comma list) are already documented. The description only adds the latest-vs-historical framing for the optional date and implies USD as a default via the example; it does not explain how base and symbols interact.

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 resource (currency exchange rates) and states the data source (ECB reference rates via Frankfurter). A sibling named fx_convert plausibly overlaps with the 'conversion' phrasing, and the description never distinguishes itself from it, so the purpose is clear but not fully de-conflicted.

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?

Gives concrete use cases (price conversion, invoicing, travel budgets) and a mode choice ('Latest rates or historical by date'), which is clear context for selection. It stops short of any exclusion or explicit alternative — notably it does not say when to use fx_convert instead.

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