Retrieves current currency exchange rates for a specified base currency, enabling quick conversions and financial calculations without requiring an API key.
Get latest currency exchange rates for a base currency. Works without API key using the free tier.
| Name | Required | Description | Default |
|---|---|---|---|
| base | No | Base currency code (default USD) | |
| api_key | No | ExchangeRate-API key (or set EXCHANGERATE_API_KEY). Optional for latest rates. |
Changes observed during successful MCP inspections.
v0.1.9v0.1.5Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, open-world, non-destructive behavior, and the description adds the one thing they cannot: authentication/cost context, namely that the free tier needs no API key and a key is optional. It stops short of describing rate source, refresh cadence, or coverage of currencies.
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?
Two short sentences with the core action front-loaded and no filler. The second sentence is genuinely load-bearing (auth/cost), though the definition is thin enough that it could have afforded one more clause on return shape.
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 simple two-optional-param read tool with annotations and full schema coverage, the essentials are present. What is missing is any indication of what the response contains (rate map vs. metadata) and the expected update frequency, which matters because there is no output schema.
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%, with both 'base' (default USD) and 'api_key' documented inline, so the schema does the heavy lifting. The description adds only the indirect hint that api_key is optional; it gives no format or default details beyond the schema.
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 and resource: retrieve the latest exchange rates for a given base currency. The purpose is unambiguous, but the description never distinguishes it from the many rate-fetching siblings (exchangerate_historical, exchangerate_convert, er_latest_rates, frankfurter_latest, forex_latest, currency_api_rates), so an agent gets no help choosing among them.
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?
Mentions that it works without an API key on the free tier, which hints at a usable default, but there is no explicit when-to-use/when-not-to-use guidance or pointer to a sibling for historical or conversion needs. 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.