List all nonce keys that have been used (have nonce > 0) for an address.
AI agents call list_active_nonce_keys to retrieve information from Tempo without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves historical nonce key information for an address without creating, modifying, deleting, or executing any state-changing operations. It is a simple informational query that provides transparency into past transactions but cannot alter blockchain state or trigger payments.
From the tool's definition Tool description states 'List all nonce keys' which is a retrieval operation with no modifications. The verb 'list' and the data being retrieved (nonce keys that have been used) are read-only queries.
Documented attack patterns abuse exactly the kind of access list_active_nonce_keys gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Tempo, and nothing reaches the server without passing your rules. This is the rule we recommend for list_active_nonce_keys:
{
"version": "1",
"default": "deny",
"tools": {
"list_active_nonce_keys": {}
}
}list_active_nonce_keys is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all nonce keys that have been used (have nonce > 0) for an address. It is categorised as a Read tool in the Tempo MCP Server, which means it retrieves data without modifying state.
Register the Tempo MCP server in PolicyLayer and add a rule for list_active_nonce_keys: 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 Tempo. Nothing to install.
list_active_nonce_keys 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 list_active_nonce_keys 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 list_active_nonce_keys. 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.
list_active_nonce_keys is provided by the Tempo MCP server (arome3/tempo-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Tempo, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
61 Tempo tools catalogued and risk-classified — across an index of 43,000+ MCP servers.