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Agent Discovery Protocol ADP

Discover The Agent Discovery Protocol (ADP) is a layered protocol, currently at v1.1, for discovering, verifying, and interacting with AI agents on the internet [1]. It is an individual IETF Internet-Draft (not adopted by any working group), revision -02, dated 18 June 2026 [1].

Overview

ADP's organizing idea is escalation: "if SVCB answers your question, do not issue an HTTP request; if Well-Known suffices, do not open a WebSocket" [1]. It is explicitly a three-layer stack. Layer 1 is DNS discovery, and rather than redefine it, ADP delegates entirely to the separate DNS-AID Internet-Draft (see dns-aid), reusing its SVCB records, its well-known/cap/cap-sha256 SvcParamKeys, and its DANE TLSA-based endpoint authentication [1]. Layer 2 is a well-known JSON metadata document, published by default at /.well-known/agent.json, containing identity, capability, relationship, security-policy and endpoint-map blocks [1]. Layer 3 covers interaction endpoints: an HTML landing page at the domain root with embedded JSON-LD structured data for human-facing discovery, plus a WebSocket transport -- the Agent Gateway Protocol (AGP) -- for real-time inter-agent messaging authenticated with Ed25519 signatures [1]. A TXT+SRV fallback exists for organizations that cannot deploy SVCB records [1].

ADP does not itself mint a new DNS mechanism (Layer 1 is DNS-AID verbatim) and does not define the internal schema of whatever protocol Layer 3 ultimately hands off to (MCP, A2A, etc. remain external, similar to ARD's artifact-agnostic envelope) [1]. Because it explicitly reuses DNS-AID, the two drafts should be read together rather than as fully independent proposals: ADP's Layer 1 section is a summary that points back to the normative DNS-AID text.

Current state: revision -02 was published 18 June 2026, expiring 20 December 2026 unless refreshed, and its "Changes from -00" section (part of the table of contents) indicates it is still actively being revised rather than stable [1]. A single-author reference implementation was located at github.com/harrylian8766/adp-protocol (5 stars, 1 fork, fetched 2026-09-06): a Node.js SDK and CLI implementing all three layers (SVCB-first DNS discovery aligned with DNS-AID's SvcParamKeys, the agent.json builder, HTML landing-page generation, and Ed25519 verification), published under a CC0 protocol license / MIT SDK license [2]. This is a solo hobbyist project rather than a vendor or standards-body implementation, so implementation is recorded as prototype rather than shipping; no independent deployment or adopter evidence was located, so adoption remains unmeasured.

What is disputed or unknown: whether ADP's Layer 2/3 additions (the well-known JSON schema, the WebSocket AGP transport) will be adopted independently of whether DNS-AID itself is adopted, since the two are only loosely coupled (an implementer could deploy DNS-AID without ADP's higher layers, or vice versa using the TXT+SRV fallback); and how ADP's /.well-known/agent.json relates to the similarly-named but structurally different /.well-known/agent fallback defined by the unrelated AID specification (see aid) -- both use the word "agent" in a well-known path but are not the same document format.

Discovery and probe

Layer 1 DNS-AID (SVCB/TLSA), Layer 2 well-known JSON metadata, Layer 3 HTML landing page + JSON-LD + WebSocket (Agent Gateway Protocol) · /.well-known/agent.json

GET https://{origin}/.well-known/agent.json
parse:     200 response is a JSON document with identity/endpoints/capabilities/security top-level blocks
on absent: Domain does not publish ADP Layer 2 metadata; check for a DNS-AID SVCB record with a well-known SvcParamKey as a possible Layer 1-only deployment

Live check run by the MCP probe: GET /.well-known/agent.json. An ADP agent.json has identity and endpoints blocks.

{
 "path": "/.well-known/agent.json",
 "expect": {
  "json_keys": [
   "identity",
   "endpoints"
  ]
 },
 "note": "An ADP agent.json has identity and endpoints blocks."
}

History

Instances

Every instance with its source is listed on the instances page.

See also

References

  1. draft-pro-adp-agent-discovery-02 (18 June 2026) defines ADP v1.1 as a three-layer stack: Layer 1 delegates entirely to DNS-AID (SVCB records), Layer 2 defines a GET-able /.well-known/agent.json metadata document, and Layer 3 defines an HTML landing page plus a WebSocket-based Agent Gateway Protocol (AGP) with Ed25519 signature authentication for real-time messaging. — https://datatracker.ietf.org/doc/html/draft-pro-adp-agent-discovery-02 (2026-06-18) VERIFIED
  2. A reference implementation exists at github.com/harrylian8766/adp-protocol (5 stars, 1 fork, fetched 2026-09-06): a Node.js SDK (protocol identifier urn:adp:1.1) implementing SVCB-first DNS discovery, TLSA/DANE, the /.well-known/agent.json builder, HTML landing-page generation, and a CLI, explicitly version-aligned with draft-pro-adp-agent-discovery-02 and cross-referencing draft-mozleywilliams-dnsop-dnsaid for SvcParamKey usage. — https://github.com/harrylian8766/adp-protocol (2026-09-06) VERIFIED

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