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mcp discovery standard

Internet-Draft · Individual Submission · March 2026

The "mcp" URI Scheme and MCP Server Discovery Mechanism

draft-serra-mcp-discovery-uri-03 · 99rig · Mumble Group

I-D Exists

This document defines the "mcp" URI scheme, a well-known URI discovery convention, and a DNS TXT fallback — enabling AI agents to autonomously discover MCP servers on any web domain without prior configuration.

1. The mcp:// URI Scheme

A machine-to-machine identifier for publicly reachable MCP servers.

// Syntax (ABNF)
mcp-URI = "mcp://" authority path-abempty [ "?" query ]

// Valid examples
mcp://example.com
mcp://api.example.com/shop
mcp://example.com:8080

2. Discovery Sequence

Upon resolving an mcp:// URI, clients MUST attempt discovery in order:

Well-Known URI REQUIRED

HTTP GET to the well-known path. 200 + valid manifest = done. 404 or timeout (5s) = proceed to step 2.

GET https://{host}/.well-known/mcp-server
Accept: application/json

DNS TXT Record FALLBACK

Query _mcp.{host} TXT. If present with v=mcp1, extract endpoint. Otherwise proceed to step 3.

_mcp.example.com IN TXT "v=mcp1; endpoint=https://example.com/mcp; auth=none"

Direct Endpoint LAST RESORT

Attempt MCP handshake at https://{host}/mcp. If it fails, no server found.

POST https://{host}/mcp

3. Manifest Schema

JSON document returned at /.well-known/mcp-server.

Field	Type	Req	Description
`mcp_version`	string	MUST	MCP spec version (e.g. "2025-06-18")
`name`	string	MUST	Human-readable server name
`endpoint`	string	MUST	URL of the MCP endpoint
`transport`	string	MUST	"http" or "stdio"
`description`	string	SHOULD	Natural language description
`auth`	object	SHOULD	{ "type": "none" \| "apikey" \| "oauth2" }
`capabilities`	array	SHOULD	["tools", "resources", "prompts"]
`categories`	array	MAY	Semantic categories
`languages`	array	MAY	ISO 639-1 codes
`coverage`	string	MAY	ISO 3166-1 country code
`contact`	string	MAY	Contact email or URL
`docs`	string	MAY	Documentation URL
`last_updated`	string	MAY	ISO 8601 timestamp
`crawl`	boolean	MAY	false to opt out of indexing

4. Reference Implementation

This domain serves a live manifest. Try it:

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

{
    "mcp_version": "2025-06-18",
    "name": "mcpstandard.dev Reference Server",
    "endpoint": "https://mcpstandard.dev/mcp",
    "transport": "http",
    "auth": { "type": "none" },
    "capabilities": ["tools", "resources"],
    "categories": ["standards", "reference", "discovery"],
    "contact": "marco.serra@mumble.group",
    "crawl": true
}

5. Implement

Server operator

# Minimal manifest
mkdir -p .well-known
cat > .well-known/mcp-server <<EOF
{
  "mcp_version": "2025-06-18",
  "name": "My Server",
  "endpoint": "https://my.domain/mcp",
  "transport": "http"
}
EOF

Client developer

# Resolve mcp://domain.com
# 1. well-known
curl -sf https://domain.com\
  /.well-known/mcp-server
# 2. DNS fallback
dig +short TXT _mcp.domain.com
# 3. direct
curl -X POST https://domain.com/mcp

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