market-ratesGet USD-based conversion rates for fiat currencies and cryptocurrencies. Optionally pass a slug (e.g. 'euro', 'us-dollar', 'bitcoin') to look up a single rate.
| Name | Required | Description | Default |
|---|---|---|---|
| slug | No | Optional: rate slug to fetch a single rate (e.g. 'us-dollar', 'euro', 'bitcoin') |
| Name | Required | Description | Default |
|---|---|---|---|
| rates | Yes |
Changes observed during successful MCP inspections.
Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Output schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Output schema / properties / rates / items / properties / currencySymbol / anyOfRemoved value: -[
- {
- "type": "string"
- },
- {
- "type": "null"
- }
-]Output schema / properties / rates / items / properties / currencySymbol / typeAdded value: +[
+ "string",
+ "null"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds that rates are USD-based and cover fiat plus crypto, but it does not disclose behavior on invalid slugs or whether omitting slug returns the full rate set. This is adequate given annotation coverage, but not rich.
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 sentences with no filler, main operation front-loaded, and the optional parameter behavior immediately follows. Every clause earns its place.
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 one-optional-parameter tool with a rich annotation set and an output schema, this description is sufficient: it states the base currency, asset classes, and the single-rate option, and the output schema covers return values. No critical invocation information is missing.
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%: the schema already documents slug as an optional single-rate lookup and gives the same example values. The tool description repeats those examples without adding new parameter meaning, so it stays at the high-coverage baseline of 3.
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 opens with a specific operation and resource: getting USD-based conversion rates for fiat currencies and cryptocurrencies. It also clearly states the optional slug behavior for single-rate lookups. It does not explicitly name a sibling to distinguish itself from, but the resource scope is specific enough to be identifiable.
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 gives no guidance on when to choose market-rates over close siblings such as price-get, price-convert, or market-global. The only usage hint is the optional slug parameter, which says how to fetch a single rate but not when this tool is the right one versus alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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