HNB (Croatian National Bank) official exchange rates for ALL foreign currencies on a given date. Croatia is in the eurozone, so every rate is quoted AGAINST THE EURO (units of foreign currency per 1 EUR). Returns rows with valuta (3-letter ISO code), srednji_tecaj (middle/reference rate), kupovni...
Part of the Hnb Hr server.
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AI agents call exchange_rates to retrieve information from Hnb Hr without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though exchange_rates only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"exchange_rates": {}
}
}See the full Hnb Hr policy for all 22 tools.
These attack patterns abuse exactly the kind of access exchange_rates gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
HNB (Croatian National Bank) official exchange rates for ALL foreign currencies on a given date. Croatia is in the eurozone, so every rate is quoted AGAINST THE EURO (units of foreign currency per 1 EUR). Returns rows with valuta (3-letter ISO code), srednji_tecaj (middle/reference rate), kupovni_tecaj (buying), prodajni_tecaj (selling), datum_primjene (apply date). Omit date for the latest applicable rates. Rate values are strings with a COMMA decimal separator (e.g. "1,164900").. It is categorised as a Read tool in the Hnb Hr MCP Server, which means it retrieves data without modifying state.
Register the Hnb Hr MCP server in PolicyLayer and add a rule for exchange_rates: 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 Hnb Hr. Nothing to install.
exchange_rates is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the exchange_rates 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 exchange_rates. 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.
exchange_rates is provided by the Hnb Hr MCP server (https://gateway.pipeworx.io/hnb-hr/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 22 Hnb Hr tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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