Updates an existing list by replacing its items with a new array. WHEN TO USE: - To modify the contents of an existing list - To add or remove items from a list - To reorder items in a list
AI agents use update_list to create or update resources in Par5 — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Par5 environment.
This tool creates or modifies data in a reversible manner (Write category). Severity is medium because the tool operates on list data structures within the MCP server context; misuse could corrupt batch processing configurations or lists of files/URLs intended for shell or agent execution, but the impact is limited to that list and typically reversible through another update_list call.
From the tool's definition Tool description states 'Updates an existing list by replacing its items with a new array' and use cases include 'modify the contents of an existing list', 'add or remove items from a list', 'reorder items in a list'.
Documented attack patterns abuse exactly the kind of access update_list gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Par5, and nothing reaches the server without passing your rules. This is the rule we recommend for update_list:
{
"version": "1",
"default": "deny",
"tools": {
"update_list": {
"limits": [
{
"counter": "update_list_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_list 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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Updates an existing list by replacing its items with a new array. WHEN TO USE: - To modify the contents of an existing list - To add or remove items from a list - To reorder items in a list. It is categorised as a Write tool in the Par5 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Par5 MCP server in PolicyLayer and add a rule for update_list: 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 Par5. Nothing to install.
update_list 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 update_list 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 update_list. 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.
update_list is provided by the Par5 MCP server (mathematic-inc/par5-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Par5, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
8 Par5 tools catalogued and risk-classified — across an index of 43,000+ MCP servers.