Compare cookies, localStorage, and sessionStorage snapshots before and after a page action.
AI agents call diff_session_state to retrieve information from JS Reverse MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool performs a comparison of browser storage state snapshots. While it observes sensitive data (cookies, storage), it does not create, modify, delete, or execute code. The core function is data retrieval and comparison, which is a Read operation.
From the tool's definition Compares snapshots of cookies, localStorage, and sessionStorage 'before and after a page action'—a diff operation that retrieves and compares state data without modifying it.
Attacks that exploit this kind of access
Compare cookies, localStorage, and sessionStorage snapshots before and after a page action. It is categorised as a Read tool in the JS Reverse MCP MCP Server, which means it retrieves data without modifying state.
Register the JS Reverse MCP server in PolicyLayer and add a rule for diff_session_state: 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 JS Reverse MCP. Nothing to install.
diff_session_state 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 diff_session_state 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 diff_session_state. 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.
diff_session_state is provided by the JS Reverse MCP server (noone-hub/jsreverser-mcp). 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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