AI agents call diff to retrieve information from Selvedge without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The diff tool appears to be a read-only operation that retrieves and displays differences between versions or changesets. It does not modify state, execute code, delete data, or move money. It fits the Read category: retrieves or queries data with no side effects.
From the tool's definition Tool name is 'diff' and sits alongside query-oriented tools like 'blame', 'history', 'changeset', and 'search' in a change-tracking system. The server description emphasizes querying history with diff as one of the retrieval operations.
Documented attack patterns abuse exactly the kind of access diff gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Selvedge, and nothing reaches the server without passing your rules. This is the rule we recommend for diff:
{
"version": "1",
"default": "deny",
"tools": {
"diff": {}
}
}diff is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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diff. It is categorised as a Read tool in the Selvedge MCP Server, which means it retrieves data without modifying state.
Register the Selvedge MCP server in PolicyLayer and add a rule for diff: 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 Selvedge. Nothing to install.
diff 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 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. 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 is provided by the Selvedge MCP server (masondelan/selvedge). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Selvedge, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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7 Selvedge tools catalogued and risk-classified — across an index of 43,000+ MCP servers.