AI agents use browser_file_upload to create or update resources in Better Playwright MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Better Playwright MCP environment.
File upload creates new data on a remote server or web application. It is a Write action (not Destructive or Execute by itself), but carries high severity because an AI agent could upload sensitive, malicious, or large volumes of files to arbitrary targets, potentially causing data leakage or abuse of upload endpoints.
From the tool's definition 'Upload one or multiple files' — the tool writes/sends files to a remote endpoint via browser interaction
Documented attack patterns abuse exactly the kind of access browser_file_upload gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Better Playwright MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for browser_file_upload:
{
"version": "1",
"default": "deny",
"tools": {
"browser_file_upload": {
"limits": [
{
"counter": "browser_file_upload_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}browser_file_upload 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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Upload one or multiple files. It is categorised as a Write tool in the Better Playwright MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Better Playwright MCP server in PolicyLayer and add a rule for browser_file_upload: 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 Better Playwright MCP. Nothing to install.
browser_file_upload 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 browser_file_upload 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 browser_file_upload. 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.
browser_file_upload is provided by the Better Playwright MCP server (livoras/better-playwright-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Better Playwright MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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29 Better Playwright MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.