AI agents call get_instances to retrieve information from Scrapybara MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool only queries and lists currently active instances. It has no side effects, does not execute commands, does not modify state, and does not delete resources. It is a straightforward informational retrieval operation, making it a Read category risk with low severity since disclosure of instance list information poses minimal immediate threat.
From the tool's definition Tool name 'get_instances' and description 'Get all running Scrapybara instances' indicate a read-only query operation that retrieves state information without modifying, executing, or deleting anything.
Documented attack patterns abuse exactly the kind of access get_instances gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Scrapybara MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for get_instances:
{
"version": "1",
"default": "deny",
"tools": {
"get_instances": {}
}
}get_instances is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get all running Scrapybara instances. It is categorised as a Read tool in the Scrapybara MCP MCP Server, which means it retrieves data without modifying state.
Register the Scrapybara MCP server in PolicyLayer and add a rule for get_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 Scrapybara MCP. Nothing to install.
get_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 get_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 get_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.
get_instances is provided by the Scrapybara MCP server (scrapybara/scrapybara-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Scrapybara 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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5 Scrapybara MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.