I used the same url for two different postings.
Resolves real-time global foreign exchange fiat rates ($0.0005 USDC)
| Name | Required | Description | Default |
|---|---|---|---|
| baseCurrency | No | Base currency ticker symbol (default USD) | USD |
| Name | Required | Description | Default |
|---|---|---|---|
| base | No | Base currency ticker | |
| rates | Yes | Key-value pair of fiat rates | |
| success | Yes | Query status |
Changes observed during successful MCP inspections.
Input schema / properties / baseCurrency / descriptionAdded value: +"Base currency ticker symbol (default USD)"Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "base": {
+ "description": "Base currency ticker",
+ "type": "string"
+ },
+ "rates": {
+ "description": "Key-value pair of fiat rates",
+ "type": "object"
+ },
+ "success": {
+ "description": "Query status",
+ "type": "boolean"
+ }
+ },
+ "required": [
+ "success",
+ "rates"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint, lowering the burden on the description. The description adds real-time behavior and a possible $0.0005 USDC cost, but does not explain rate sources, update frequency, or what the resolved result contains. This is adequate 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?
The description is a single efficient sentence with the core purpose front-loaded. The '$0.0005 USDC' parenthetical is compact but unclear in meaning, slightly reducing structural clarity.
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 read-only tool with an output schema, the description is mostly sufficient. However, it does not explain the expected relationship between baseCurrency and the returned rates, nor clarify the ambiguous cost/pricing parenthetical, leaving some context gaps.
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%, so the baseCurrency parameter is already fully documented with its default. The description does not add extra meaning beyond what the schema provides, keeping this at baseline.
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 states a clear verb ('Resolves') and resource ('real-time global foreign exchange fiat rates'), which distinguishes it from crypto/dex oracles among siblings. The parenthetical '$0.0005 USDC' adds ambiguity about whether it is a cost or a rate, preventing a perfect score.
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 real-time fiat forex focus implies when the tool should be used, but there is no explicit guidance about when not to use it or which sibling alternatives (e.g., data_feeds, arc_dex_oracle) might be more appropriate. Usage context is present but left to inference.
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.