replace · TinyFn MCP: Risk & Policy

WHAT IT DOES

What replace does on TinyFn

AI agents use replace to create or update resources in TinyFn — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your TinyFn environment.

PARAMETERS

Parameter	Type	Required	Description
`text`	string	Yes	The original text
`search`	string	Yes	Text to search for
`replacement`	string	—	Replacement text

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why replace needs a policy

This tool modifies text content reversibly by replacing specified substrings. It is a text manipulation utility that creates or modifies data (the modified text string), fitting the Write category. The operation is fully reversible—replaced text can be replaced again.

From the tool's definition Tool name 'replace' and description 'Replace occurrences in text' indicate text modification without deletion or execution of external operations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

replace Rate-limited

replace 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches TinyFn, so you can run agents against it safely.

FAQ

Questions about replace

What does the replace tool do? +

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

What parameters does replace accept? +

replace accepts 3 parameters: text, search, replacement. Required: text, search. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on replace? +

Register the TinyFn MCP server in PolicyLayer and add a rule for replace: 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 TinyFn. Nothing to install.

What risk level is replace? +

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

Can I rate-limit replace? +

Yes. Add a rate_limit block to the replace 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 replace completely? +

Set action: deny in the PolicyLayer policy for replace. 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 replace? +

replace is provided by the TinyFn MCP server (https://api.tinyfn.io/mcp/all/). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.