AI agents call check_http3 to retrieve information from Intodns without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves information about a domain's HTTP/3 and QUIC support by querying HTTP headers and DNS records. It is a passive read operation with no ability to modify, delete, or execute arbitrary code. The blast radius of misuse is minimal—an agent could only enumerate technical capabilities of domains.
From the tool's definition Tool is described as 'Read-only' and performs a check by reading HTTP response headers and DNS records. No modifications or side effects are performed.
Attacks that exploit this kind of access
Read-only HTTP/3 + QUIC support check for a domain. Combines three signals: Alt-Svc HTTP response header advertising h3, HTTPS/SVCB DNS records advertising alpn=\. It is categorised as a Read tool in the Intodns MCP Server, which means it retrieves data without modifying state.
Register the Intodns MCP server in PolicyLayer and add a rule for check_http3: 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 Intodns. Nothing to install.
check_http3 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 check_http3 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 check_http3. 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.
check_http3 is provided by the Intodns MCP server (rosconl/intodns-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
check_http3 is one line of Intodns's registry record.
The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.
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