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Novarithm Agent Hub: trust and commerce checks

by com.novarithm.www
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fx_xaf_zar

[PAID $0.002 USDC/call, x402, eip155:8453] Official XAF/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_xaf_zar"
  }
}

Input Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A3.8/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and does well: it discloses the paid model ($0.002 USDC/call via x402 on eip155:8453), the authoritative source (ECB fixings), the peg fallback behavior, and that output is deterministic with no estimation. What it omits is edge behavior — whether a non-fixing day returns the prior fixing or an error — and any failure/refund semantics for the paid call.

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?

A compact single sentence plus a bracketed payment preamble; nothing is redundant. The payment/x402 metadata is front-loaded ahead of the purpose, which slightly slows an agent scanning for what the tool does, but the total length is well controlled.

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 zero-parameter tool with no output schema and no annotations, the description covers the essentials an agent needs: what rate, which source, what accompanying fields (rate date, method, attribution), and the determinism guarantee. Only the exact response shape and non-trading-day behavior remain unstated.

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 zero parameters, so there is no schema meaning to add; baseline 4 applies. The description adds no parameter confusion and correctly implies a no-argument call.

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

Purpose4/5

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

States a specific verb and resource: 'Official XAF/ZAR reference rate' with the source ('latest European Central Bank fixing') and a peg fallback. The currency pair is unambiguous and matches the tool name, so an agent can distinguish it from the other ~400 fx_* siblings by pair. It stops short of naming a differentiated sibling (e.g. fx_convert or the inverse fx_zar_xaf), which keeps it from a 5.

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?

Usage is only implied: 'reference rate' and 'deterministic, sourced, no estimate' suggest it is for authoritative reference lookups rather than conversion arithmetic, but the description never says when to prefer this over fx_convert, fx_latest, or the inverse fx_zar_xaf. No exclusions or prerequisites are stated beyond the implicit payment requirement.

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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