Check which Chrome Extension APIs are available to the extension
AI agents call extension_tool_check_available_apis to retrieve information from WebMCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool performs discovery/inspection of the extension's capabilities by querying which APIs are accessible. This is a non-destructive read operation with no side effects. The information returned could inform subsequent tool calls, but the tool itself only retrieves metadata.
From the tool's definition Tool name and description indicate a query operation: 'Check which Chrome Extension APIs are available' — this retrieves information about available APIs without modifying, executing, or deleting anything.
Documented attack patterns abuse exactly the kind of access extension_tool_check_available_apis gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and WebMCP, and nothing reaches the server without passing your rules. This is the rule we recommend for extension_tool_check_available_apis:
{
"version": "1",
"default": "deny",
"tools": {
"extension_tool_check_available_apis": {}
}
}extension_tool_check_available_apis is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Check which Chrome Extension APIs are available to the extension. It is categorised as a Read tool in the WebMCP MCP Server, which means it retrieves data without modifying state.
Register the Web MCP server in PolicyLayer and add a rule for extension_tool_check_available_apis: 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 WebMCP. Nothing to install.
extension_tool_check_available_apis 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 extension_tool_check_available_apis 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 extension_tool_check_available_apis. 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.
extension_tool_check_available_apis is provided by the Web MCP server (miguelspizza/webmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from WebMCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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13 WebMCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.