merge_json · TinyFn MCP: Risk & Policy

WHAT IT DOES

What merge_json does on TinyFn

AI agents use merge_json 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
`deep`	boolean	—	Deep merge nested objects
`json1`	string	Yes	Base JSON object
`json2`	string	Yes	JSON object to merge

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why merge_json needs a policy

Merging JSON objects creates or modifies data structures reversibly. This is a Write operation rather than Read (it modifies, not just retrieves), Execute (it doesn't run arbitrary code or trigger external operations), or Destructive (the operation is reversible and doesn't delete data).

From the tool's definition Tool name 'merge_json' and description 'Merge two JSON objects' indicate creation/modification of data. The operation combines two JSON objects into one, which is a reversible data transformation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

merge_json Rate-limited

merge_json 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": {
    "merge_json": {
      "limits": [
        {
          "counter": "merge_json_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 merge_json

What does the merge_json tool do? +

Merge two JSON objects. 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 merge_json accept? +

merge_json accepts 3 parameters: deep, json1, json2. Required: json1, json2. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on merge_json? +

Register the TinyFn MCP server in PolicyLayer and add a rule for merge_json: 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 merge_json? +

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

Can I rate-limit merge_json? +

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

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

merge_json 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.