AI agents call regex_test to retrieve information from Basic without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs pattern matching validation on a string argument and returns a boolean result. It retrieves no persistent data, modifies nothing, executes no code or commands, and has no side effects. It is a pure deterministic utility function for string validation, consistent with the server's stated purpose of providing helpers for operations LLMs struggle with.
From the tool's definition Tool name 'regex_test' and description 'Test if a string matches a regular expression pattern' indicate a query operation that tests/validates input without modifying data or executing external operations.
Attacks that exploit this kind of access
Test if a string matches a regular expression pattern. It is categorised as a Read tool in the Basic MCP Server, which means it retrieves data without modifying state.
Register the Basic MCP server in PolicyLayer and add a rule for regex_test: 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 Basic. Nothing to install.
regex_test 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 regex_test 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 regex_test. 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.
regex_test is provided by the Basic MCP server (msilverblatt/basic-mcp). 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.
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