update_custom_item

THE RISK

Medium Risk

Why update_custom_item needs a policy

This tool modifies existing data (custom items) in a reversible manner, fitting the Write category. Severity is medium because it affects user fitness/training data in Intervals.icu, which is personal but not financial or destructive. Confidence is slightly lower (0.75) due to the empty description, which prevents full assessment of what 'custom_item' encompasses and what constraints exist on updates.

From the tool's definition Tool name 'update_custom_item' indicates modification of data. The description is empty, but context from sibling tools (add_or_update_event, add_or_update_note, create_custom_item) shows this server manages fitness data that can be created, updated, and…

Documented attack patterns abuse exactly the kind of access update_custom_item gives an agent:

POLICY

How to control update_custom_item

PolicyLayer is an MCP gateway — it sits between your AI agents and Intervals Icu MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for update_custom_item:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "update_custom_item": {
      "limits": [
        {
          "counter": "update_custom_item_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

update_custom_item 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.

Create a free account and register Intervals Icu MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Intervals Icu MCP Server tools

Destructive delete_custom_item Delete a custom item for an athlete from Intervals.icu Args: item_id: The cus Destructive delete_event Delete event for an athlete from Intervals.icu Args: athlete_id: The Intervals Destructive delete_events_by_date_range Delete events for an athlete from Intervals.icu in the specified date range. Args: Execute register_tools Register all MCP tools with the FastMCP server instance. This function imports all to Write add_activity_message Add a message (note/comment) to an activity on Intervals.icu Args: activity_i Write add_or_update_event add_or_update_event Write add_or_update_note Add or update a plain text note (category NOTE) on the Intervals.icu calendar. Args: Write create_custom_item create_custom_item

All 21 Intervals Icu MCP Server tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about update_custom_item

What does the update_custom_item tool do? +

update_custom_item. It is categorised as a Write tool in the Intervals Icu MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_custom_item? +

Register the Intervals Icu MCP Server MCP server in PolicyLayer and add a rule for update_custom_item: 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 Intervals Icu MCP Server. Nothing to install.

What risk level is update_custom_item? +

update_custom_item is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit update_custom_item? +

Yes. Add a rate_limit block to the update_custom_item 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.

How do I block update_custom_item completely? +

Set action: deny in the PolicyLayer policy for update_custom_item. 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.

What MCP server provides update_custom_item? +

update_custom_item is provided by the Intervals Icu MCP Server MCP server (mvilanova/intervals-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Intervals Icu MCP Server tool call.

Start from Intervals Icu MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →