mcpstandard.dev

The mcp:// URI Scheme and MCP Server Discovery Mechanism

Reference implementation and specification for draft-serra-mcp-discovery-uri-03 — the latest version.

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What is this?

This repository contains:

• The IETF Internet Draft defining mcp:// as a URI scheme for MCP server discovery
• A live reference implementation at mcpstandard.dev
• A Python client library for resolving mcp:// URIs
• A validator for /.well-known/mcp-server manifests

The Problem

Today, connecting an AI agent to an MCP server requires manual configuration. No standard mechanism exists for an agent to discover which web domains expose an MCP server starting from a domain name alone.

The Solution

Three components work together:

1. mcp:// URI scheme — identifies an MCP server by domain
2. /.well-known/mcp-server — a JSON manifest exposing server metadata
3. DNS TXT fallback — _mcp.domain TXT "v=mcp1; endpoint=..."

Quick Start — Expose your MCP server

mkdir -p .well-known
echo '{
  "mcp_version": "2025-06-18",
  "name": "My MCP Server",
  "endpoint": "https://mydomain.com/mcp",
  "transport": "http"
}' > .well-known/mcp-server

Quick Start — Resolve an mcp:// URI

# Step 1 — well-known
curl -sf https://domain.com/.well-known/mcp-server

# Step 2 — DNS fallback
dig +short TXT _mcp.domain.com

# Step 3 — direct
curl -X POST https://domain.com/mcp

Live Reference Implementation

curl -s https://mcpstandard.dev/.well-known/mcp-server | python3 -m json.tool

IETF Draft

Version	URL
-00	https://datatracker.ietf.org/doc/draft-serra-mcp-discovery-uri/00/
-01	https://datatracker.ietf.org/doc/draft-serra-mcp-discovery-uri/01/
-02	https://datatracker.ietf.org/doc/draft-serra-mcp-discovery-uri/02/
-03	https://datatracker.ietf.org/doc/draft-serra-mcp-discovery-uri/03/ ← latest

Related Work

• SEP-1649 — MCP Server Cards proposal by MCP maintainers
• GitHub Discussion #2462 — Coordination thread

Author

Marco Serra — Mumble Group — Milan, Italy
marco.serra@mumble.group | https://mcpstandard.dev