get_nonce_for_key

THE RISK

Low Risk

Why get_nonce_for_key needs a policy

This tool queries and returns the current nonce value for transaction sequencing purposes. It performs a read-only operation that neither modifies state, executes external operations, nor affects financial holdings. The nonce is informational metadata needed to construct valid transactions, but retrieving it causes no state change or irreversible action.

From the tool's definition Tool name is 'get_nonce_for_key' and description states 'Get the current transaction nonce' — a retrieval operation with no side effects.

Documented attack patterns abuse exactly the kind of access get_nonce_for_key gives an agent:

POLICY

How to control get_nonce_for_key

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 get_nonce_for_key:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "get_nonce_for_key": {}
  }
}

get_nonce_for_key is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Tempo — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

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Go deeper

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about get_nonce_for_key

What does the get_nonce_for_key tool do? +

Get the current transaction nonce for a specific nonce key (0-255). It is categorised as a Read tool in the Tempo MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on get_nonce_for_key? +

Register the Tempo MCP server in PolicyLayer and add a rule for get_nonce_for_key: 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.

What risk level is get_nonce_for_key? +

get_nonce_for_key is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit get_nonce_for_key? +

Yes. Add a rate_limit block to the get_nonce_for_key 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.

How do I block get_nonce_for_key completely? +

Set action: deny in the PolicyLayer policy for get_nonce_for_key. 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.

What MCP server provides get_nonce_for_key? +

get_nonce_for_key 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.

Enforce policy on every Tempo tool call.

Start from Tempo, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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