Exact key lookup. Returns the stored value or not_found.
AI agents call recall_by_key to retrieve information from Nexus Core without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a simple data lookup operation by key and returns either the stored value or a not_found response. It is purely informational with no capability to modify, delete, or execute operations. The severity is low because even if an AI agent misuses it by looking up sensitive keys, the damage is limited to information disclosure rather than data modification or destruction.
From the tool's definition Tool description states 'Exact key lookup. Returns the stored value or not_found.' - a retrieval operation with no side effects.
Attacks that exploit this kind of access
Exact key lookup. Returns the stored value or not_found. It is categorised as a Read tool in the Nexus Core MCP Server, which means it retrieves data without modifying state.
Register the Nexus Core MCP server in PolicyLayer and add a rule for recall_by_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 Nexus Core. Nothing to install.
recall_by_key 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 recall_by_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.
Set action: deny in the PolicyLayer policy for recall_by_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.
recall_by_key is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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