AI agents use save_patch to create or update resources in Pure Data MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Pure Data MCP Server environment.
This tool creates or modifies data (the patch file) on the filesystem. It is reversible—the previous version can be recovered from backups or version control—so it does not qualify as Destructive. While it persists state changes, the operation itself is not an Execute (which runs code with side effects) or a Read operation. Save operations are typically Write-category.
From the tool's definition Tool name is 'save_patch' and description states 'Save the current Pd patch', indicating it writes/modifies files on disk.
Documented attack patterns abuse exactly the kind of access save_patch gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Pure Data MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for save_patch:
{
"version": "1",
"default": "deny",
"tools": {
"save_patch": {
"limits": [
{
"counter": "save_patch_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}save_patch stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Save the current Pd patch. It is categorised as a Write tool in the Pure Data MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Pure Data MCP Server MCP server in PolicyLayer and add a rule for save_patch: 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 Pure Data MCP Server. Nothing to install.
save_patch is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the save_patch 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 save_patch. 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.
save_patch is provided by the Pure Data MCP Server MCP server (nikmaniatis/pd-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Pure Data MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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11 Pure Data MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.