List all active browser instances
AI agents call list_browser_instances to retrieve information from MCP Developer Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a read-only operation—it queries and returns a list of active browser instances. There are no side effects, no data modification, no code execution, and no irreversible actions. It simply retrieves state information, fitting the Read category definition of retrieving or querying data with no side effects.
From the tool's definition Tool name 'list_browser_instances' and description 'List all active browser instances' indicate a query operation that retrieves information about existing browser instances without modification, deletion, or execution of commands.
Attacks that exploit this kind of access
List all active browser instances. It is categorised as a Read tool in the MCP Developer Server MCP Server, which means it retrieves data without modifying state.
Register the MCP Developer Server MCP server in PolicyLayer and add a rule for list_browser_instances: 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 MCP Developer Server. Nothing to install.
list_browser_instances is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_browser_instances 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 list_browser_instances. 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.
list_browser_instances is provided by the MCP Developer Server MCP server (ra86-dev/mcpdev-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
Teams ship this data inside their own products. See what a licence covers →