browser_upload_file

Upload a workspace-readable file into a file input, preferably using a Browser V2 ref from browser_snapshot

SERVERCoWork OS SOURCECoWork-OS/CoWork-OS

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/cowork-os/browser-upload-file.md

WHAT IT DOES

What browser_upload_file does on CoWork OS

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

RISK

Why browser_upload_file is rated Medium

The tool writes data (uploads a file) into a web form input, which is reversible and creates/modifies workspace state. It is not destructive (file can be replaced), not financial, and not execute-level code running. While it involves browser automation (which can be Execute-category), the specific action here is file upload rather than arbitrary command execution.

From the tool's definition Tool description states 'Upload a workspace-readable file into a file input', indicating file creation/modification within the workspace context via browser interaction.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs browser_upload_file safely

PolicyLayer is an MCP gateway: it sits between your AI agents and CoWork OS, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For browser_upload_file, this is the rule to start with:

browser_upload_file Rate-limited

browser_upload_file 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": {
    "browser_upload_file": {
      "limits": [
        {
          "counter": "browser_upload_file_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect CoWork OS, apply this rule, and every browser_upload_file call is checked against it from then on.

FAQ

Questions about browser_upload_file

What does the browser_upload_file tool do? +

Upload a workspace-readable file into a file input, preferably using a Browser V2 ref from browser_snapshot. It is categorised as a Write tool in the CoWork OS MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on browser_upload_file? +

Register the CoWork OS MCP server in PolicyLayer and add a rule for browser_upload_file: 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 CoWork OS. Nothing to install.

What risk level is browser_upload_file? +

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

Can I rate-limit browser_upload_file? +

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

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

browser_upload_file is provided by the CoWork OS MCP server (CoWork-OS/CoWork-OS). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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