AI agents call read_screen to retrieve information from Pharo Smalltalk Interop without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool reads screen state or visual output from the Pharo Smalltalk image without modifying any data. This is consistent with Read category operations (retrieve/query data with no side effects). Even though the description is uninformative, the name strongly suggests a passive observation operation. Severity is low because screen reads cannot damage data or systems.
From the tool's definition Tool name 'read_screen' clearly indicates data retrieval with no modification capability. Description is empty, which lowers confidence slightly.
Documented attack patterns abuse exactly the kind of access read_screen gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Pharo Smalltalk Interop, and nothing reaches the server without passing your rules. This is the rule we recommend for read_screen:
{
"version": "1",
"default": "deny",
"tools": {
"read_screen": {}
}
}read_screen is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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read_screen. It is categorised as a Read tool in the Pharo Smalltalk Interop MCP Server, which means it retrieves data without modifying state.
Register the Pharo Smalltalk Interop MCP server in PolicyLayer and add a rule for read_screen: 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 Pharo Smalltalk Interop. Nothing to install.
read_screen 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 read_screen 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 read_screen. 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.
read_screen is provided by the Pharo Smalltalk Interop MCP server (mumez/pharo-smalltalk-interop-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Pharo Smalltalk Interop, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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23 Pharo Smalltalk Interop tools catalogued and risk-classified — across an index of 43,000+ MCP servers.