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

With no annotations, the description carries the full burden and does add real context: the data source (ECB/Frankfurter), that no API key is needed, the return payload (converted amount plus exact rate applied), and payment terms ($0.02/call via x402, USDC on eip155:8453). Missing only freshness/rate-limit expectations and that this is a non-destructive read/compute operation.

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 core action and scope, and the data-source and pricing details follow logically. Slightly redundant — the third sentence largely restates the first two — but nothing is wasteful enough to harm usability.

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, no-annotation, no-output-schema tool, the description is largely complete: action, data source, return values, and pricing are all covered. The one material gap an agent still faces is the currency-code input format, which is left to inference.

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 description coverage is 100% but the field descriptions are placeholder-level ("From", "To", "Amount"), so the schema adds little real meaning. The description helps by scoping the domain to "30+ fiat currencies" but never states the expected currency-code format (e.g., ISO codes like USD/EUR), which is the key ambiguity for from/to.

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 (convert) and resource (amount between 30+ fiat currencies) with the data source (ECB reference rates via Frankfurter). It implicitly distinguishes itself from rate-listing siblings like live_exchange_rates by framing itself as the conversion tool, but never names an alternative sibling explicitly.

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?

"Use this when an agent needs to convert any amount at ECB reference rates" gives a clear use context, and the "instead of guessing from memory" framing clarifies why the agent should call it. However, it does not name alternatives (e.g., live_exchange_rates when only a rate table is needed) or exclusions, so it stops short of full routing guidance.

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