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Novarithm Agent Hub: trust and commerce checks

by com.novarithm.www
OverviewDiscussionsAdmin

fx_cad_zar

[PAID $0.002 USDC/call, x402, eip155:8453] Official CAD/ZAR reference rate: latest European Central Bank fixing (or the official peg when ZAR is pegged), with the rate date, the method (direct, cross via EUR or peg-derived) and the source attribution. Deterministic, sourced, no estimate.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "fx_cad_zar"
  }
}

Input Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.1/5.0
Behavior4/5

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

With no annotations at all, the description carries the full behavioral burden and does well: it discloses the paywall, price, payment protocol and chain, the data provenance (ECB fixing, or official peg when ZAR is pegged), and that results are deterministic and sourced rather than estimated. It does not say what happens on payment failure, whether responses are cacheable, or the response format, which keeps it short of a 5 for a tool with zero annotation coverage.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

One dense sentence plus a short qualifier; nothing is padded. The pricing/transport bracket is front-loaded ahead of the actual purpose, which is defensible for a paywalled endpoint but slightly delays the core identification.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a parameterless single-value lookup with no output schema, the description covers provenance, pricing, determinism, and the fields the agent will receive. The only omissions are response format and failure/retry behavior, which are minor at this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes no parameters, so the schema baseline is 4. The description sensibly spends its words on the return content (rate date, derivation method, source attribution) rather than inventing parameter detail that does not exist.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific resource and verb ('Official CAD/ZAR reference rate', 'latest European Central Bank fixing') and pins the exact pair, so an agent can distinguish it from the hundreds of sibling fx_<base>_<quote> tools and from fx_latest/fx_convert/fx_timeseries without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description tells the agent this is a PAID call ($0.002 USDC, x402, eip155:8453), which is a real usage constraint, and implies the appropriate case (an official reference/fixing rate rather than an estimate). However, it never states when to prefer a sibling — e.g. fx_convert for conversion math or fx_timeseries for history — so the agent must infer the routing.

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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