MCP Registry Architecture: DNS-Based Discovery for AI Agents
Version 1.1 · February 2026
This paper proposes a lightweight, deployable architecture for solving the agent discovery problem in Model Context Protocol (MCP) ecosystems. The core proposal is a DNS-based convention — an _mcp TXT record — that points any compliant AI agent to an organisation’s MCP registry. DNS-based discovery is not new: MX, SRV, _dmarc, and WebFinger all use the same pattern. The novelty here is the specific convention for MCP, the design decision to make the registry itself an MCP server (requiring no special client code), and a fully serverless reference implementation.
No novel infrastructure is required. The proposal composes existing, operationally proven technologies into a governance-first discovery layer that any organisation can deploy in a day and run for under $5 per month at typical registry volumes.
What the Paper Covers
- The agent discovery problem and why manual configuration does not scale
- The
_mcpDNS TXT record convention and its field specification - A fully serverless registry architecture: Amazon CloudFront, Lambda@Edge, and DynamoDB Global Tables
- Public and private server access control enforced at the edge
- Security considerations including DNSSEC, JWT authentication, and prompt injection via registry
- A complete implementation guide with deployment steps and cost analysis
- Relationship to the official MCP registry, SEP #1959, NANDA, A2A, and WebFinger
- A live reference implementation at mcp.mariothomas.com
Download
The paper is available in PDF, Markdown, and Word formats from the companion GitHub repository:
github.com/mariothomas/mcp-dns-registry
Versions
| Version | Date | Changes |
|---|---|---|
| 1.0 | 25 February 2026 | Initial publication. |
| 1.1 | March 2026 | Added Section 2.3 — What This Proposal Does Not Solve — clarifying that the _mcp DNS record addresses discovery only, and that authentication, authorisation, and tool capability enumeration are explicitly out of scope for the DNS layer. |
Reference Implementation
A working implementation is live at mcp.mariothomas.com, including a queryable _mcp DNS record, a fully functional registry, and three MCP servers — public articles, public locations, and private documents with signed-URL retrieval. Source code is available in the GitHub repository.
Feedback and Collaboration
This is a discussion draft. Feedback, critique, and alternative implementations are welcomed — particularly on the DNS convention itself and on non-AWS implementations. Open an issue or discussion in the GitHub repository, or get in touch directly here.
