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

With no annotations, the description carries the transparency burden. It discloses return values (converted amount and exchange rate), data source behavior (live mid-market rates, non-ECB/Frankfurter by default), unsupported crypto pairs, and provider differences between lite tools. It does not disclose error handling or rate freshness details, but given the simplicity of the tool, this is a minor gap.

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?

Although the description is longer than typical, every sentence earns its place. It is front-loaded with the core purpose and then systematically addresses usage guidance, alternatives, and exclusions. The length is justified by the complex sibling landscape, and there is no redundant or filler content.

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?

The description is complete for a simple conversion tool: it states what it returns, when to use it, and how it differs from siblings. Since there is no output schema, the description clarifies that both the converted amount and rate are returned. It stops short of naming exact return fields, but this is not critical for a 'lite' tool.

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?

All three parameters have detailed schema descriptions with examples and case-insensitivity, so schema coverage is 100%. The description adds some context by noting 'fiat currencies' and accepting 'all major ISO 4217 currency codes', which clarifies the parameter domain but does not substantially extend the schema's 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?

The description clearly states the tool's function with a specific verb and resource: 'Converts a foreign exchange (FX) amount between two fiat currencies using live mid-market rates.' It also differentiates from siblings by naming alternative tools and their specific use cases, making the purpose unambiguous.

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?

Explicit when-to-use guidance is provided: 'Use currency_fx_lite when only the numeric result is required and the ECB/Frankfurter data source is not specifically needed.' It also gives alternatives for richer metadata (currency_convert), ECB-specific rates (currency_convert_lite), historical rates (currency_rates), and open-source rates (currency_convert_open), along with crypto exclusions. This is exemplary usage guidance.

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