Convert an amount between currencies. Live FX from exchangerate.host (free, no key). Pass an optional ISO date for historical rates. Returns {amount, from, to, rate, date, source}.
| Name | Required | Description | Default |
|---|---|---|---|
| to | Yes | ISO 4217 code, e.g. 'INR'. | |
| date | No | Optional ISO date YYYY-MM-DD for historical rate. | |
| from | Yes | ISO 4217 code, e.g. 'USD'. | |
| amount | Yes |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses the data source (exchangerate.host), that it is free and requires no API key, and that an optional date can be used for historical rates. It also mentions the return format, providing useful behavioral context. Minor omission: no mention of rate limits or API reliability.
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?
The description is three sentences with no wasted words. The first sentence immediately states the purpose, followed by key usage details. Every sentence provides necessary information efficiently.
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?
Despite having no output schema, the description explains the return structure in detail. The tool is simple with 4 parameters, all covered in the description. Sibling tools are distinct, and the description sufficiently equips an agent to select and invoke the tool correctly.
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?
The schema has 75% coverage; the description adds context for the 'date' parameter by noting it's an optional ISO date for historical rates. For the other parameters (amount, from, to), the description adds no new detail beyond the schema's own descriptions, which are already clear (e.g., 'ISO 4217 code'). Overall, value added is moderate.
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 'Convert an amount between currencies.' as the primary action, with specific verb and resource. It also mentions live FX and historical rates, but does not explicitly differentiate from sibling tools like convert_timezone or convert_unit, though the domain is distinct.
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 implies usage for currency conversion and provides context (live FX from exchangerate.host, free, no key, optional date). However, it does not specify when not to use this tool or suggest alternatives, leaving the agent to infer the appropriate context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
Each tool has a distinct purpose: currency conversion, timezone conversion, unit conversion, date difference calculation, and listing supported entities. There is no overlap, so an agent can easily choose the correct tool.
Tools follow a consistent verb_noun pattern (e.g., convert_currency, list_timezones). The only minor deviation is 'date_diff' which uses noun_noun, but it is still clear and fits the pattern of other tools.
With 6 tools, the set is well-scoped for a unit and currency converter. It covers all necessary operations without being too sparse or overwhelming.
The tools provide full conversion capabilities (currency, timezone, unit), date difference calculation, and listing helpers for timezones and units. There are no obvious gaps for the server's stated purpose.