Convert between any two fiat currencies (USD, EUR, GBP, JPY, BRL, USDC-equivalent, 160+ ISO-4217 codes) at the current mid-market rate. Returns both the rate and the converted amount, plus the rate's last update timestamp. Use when an agent needs to price a service in another currency, normalize ...
Part of the Onyx Mcp server.
Free to start. No card required.
AI agents use onyx_fx_convert to create or modify resources in Onyx Mcp. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call onyx_fx_convert repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Onyx Mcp.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"onyx_fx_convert": {
"limits": [
{
"counter": "onyx_fx_convert_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Onyx Mcp policy for all 67 tools.
These attack patterns abuse exactly the kind of access onyx_fx_convert gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Convert between any two fiat currencies (USD, EUR, GBP, JPY, BRL, USDC-equivalent, 160+ ISO-4217 codes) at the current mid-market rate. Returns both the rate and the converted amount, plus the rate's last update timestamp. Use when an agent needs to price a service in another currency, normalize multi-currency invoices, or convert x402 USDC amounts to local fiat for human-readable receipts. Powered by open.er-api.com (free tier, no key). ~150-400ms. Demo mode returns USD-EUR @ 0.92 for testing. (price: $0.002 USDC, tier: metered). It is categorised as a Write tool in the Onyx Mcp MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Onyx MCP server in PolicyLayer and add a rule for onyx_fx_convert: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Onyx Mcp. Nothing to install.
onyx_fx_convert is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the onyx_fx_convert rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for onyx_fx_convert. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
onyx_fx_convert is provided by the Onyx MCP server (https://onyx-actions.onrender.com/mcp/). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 67 Onyx Mcp tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
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