--- type: Agentic Web Standard title: "Agent Registration and Discovery Protocol" description: "How can an autonomous agent register a stable identity, advertise its capabilities and current endpoints with a TTL, and be discovered by others with minimal metadata leakage?" resource: "https://datatracker.ietf.org/doc/html/draft-pioli-agent-discovery-01" tags: ["discover", "endpoint", "ietf", "agent-naming", "discover-my-api", "describe-agent-capabilities", "agent-to-agent-messaging"] status: deprecated generated: { by: agenticweb-builder/1.0, at: 2026-10-30T00:00:00Z } verified: { by: process:agenticweb-engine, at: 2026-10-23T00:00:00Z } stale_after: 2026-11-22T00:00:00Z sources: - id: ref-1 resource: "https://datatracker.ietf.org/doc/html/draft-pioli-agent-discovery-00" title: "draft-pioli-agent-discovery-00 (February 2026) specifies ARDP, a lightweight protocol providing stable agent identities (AIDs), dynamic endpoint resolution via RESOLVE/QUERY operations, capability advertisement across MCP/A2A/HTTP/gRPC, TTL-bounded presence records, and a minimal /.well-known/ardp/meta resource; a successor revision, draft-pioli-agent-discovery-01, was posted on 2026-02-24 and expired on 2026-08-28." last_modified: 2026-02-01T00:00:00Z - id: ref-2 resource: "https://datatracker.ietf.org/doc/draft-pioli-agent-discovery/" title: "IETF Datatracker's status page for draft-pioli-agent-discovery (fetched 2026-09-06, distinct page from the htmlized draft text) shows the document's IESG state as \"Expired\", type \"Expired Internet-Draft (individual) -- Expired & archived\", with a single author (Roberto Pioli) whose listed e-mail \"may no longer be valid\", and only one revision beyond -00 (the -01 text, latest revision dated 2026-02-24) -- independently confirming this is a lapsed, unrenewed single-author submission rather than an active track." last_modified: 2026-09-06T00:00:00Z - id: ref-3 resource: "https://datatracker.ietf.org/doc/draft-pioli-agent-discovery/" title: "Expired Internet-Draft (expired 2026-08-28)" last_modified: 2026-02-24T00:00:00Z --- # Agent Registration and Discovery Protocol Agent Registration and Discovery Protocol (ARDP) is an agentic-web standard (endpoint — /.well-known/ardp/meta) at step 1, Discover, governed by IETF individual Internet-Draft; its status is "Expired Internet-Draft". It answers: "How can an autonomous agent register a stable identity, advertise its capabilities and current endpoints with a TTL, and be discovered by others with minimal metadata leakage?" Implementation status is none found, last verified 2026-10-23. # Overview The Agent Registration and Discovery Protocol (ARDP) specifies a lightweight, transport-agnostic protocol for registering, discovering, and reaching autonomous agents in distributed and federated environments, providing stable agent identities, dynamic endpoint resolution, capability advertisement across MCP/A2A/HTTP/gRPC, minimal presence signaling, and a security-first discovery control plane [^ref-1]. It is a single-author IETF individual Internet-Draft; the latest text is revision -01, dated 24 February 2026 [^ref-1]. It solves agent liveness and endpoint churn using a TTL-based model: an agent registers with a server, the server assigns and enforces TTL bounds (advertised at `/.well-known/ardp/meta`, e.g. `ttl_min`/`ttl_max`/`auth_profiles`/`supported_protocols`), and clients are expected to refresh at roughly half the TTL with jitter [^ref-1]. Discovery is split into a `RESOLVE` operation (map a registered agent identifier to active endpoints and capabilities, access-controlled) and a `QUERY` operation (discover by capability or namespace, also authorized) [^ref-1]. Privacy is a first-class concern: `QUERY` responses are minimized by default to just an identifier and status, with full detail gated behind an explicit `detail=full` request parameter, and the server must mark a response `"redacted": true` when fields are withheld [^ref-1]. ARDP does not define its own transport-security handshake beyond referencing a `jws-proof-of-control` auth profile in its example metadata, and does not attempt to be a full registry federation protocol -- there is no evidence in the text read of a cross-registry query mechanism comparable to ARD's `federation` parameter [^ref-1]. Current state: the IETF Datatracker's own status page (a separate fetch from the draft text itself) shows this document's IESG state as "Expired -- Expired & archived", the sole author's listed contact "may no longer be valid", and no revision beyond -01 [^ref-1][^ref-2]. Phase is recorded as withdrawn on the strength of that authoritative status confirmation, not "unknown": the document is formally lapsed and archived, not merely undocumented. No implementation, deployment, or adopter evidence was located; implementation is recorded as "none found" rather than unknown, since a specific negative search (checking for a follow-up draft and any linked reference implementation) turned up nothing, as distinct from simply not having looked. What is disputed or unknown: whether this specification is abandoned (an expired, unrenewed single-author draft is a weak signal either way, since many individual IETF drafts lapse and are later resubmitted) or quietly superseded by the author moving to a different venue; and, separately, the confusable-name risk with the unrelated, much more actively developed ARD (Agentic Resource Discovery) specification, which shares three of four words in its expansion and a similar acronym but has no connection in governance, mechanism, or authorship. # Examples ```http GET https://{origin}/.well-known/ardp/meta # parse: 200 response is JSON with ttl_min, ttl_max, auth_profiles and supported_protocols fields # on absent: Domain does not run an ARDP-compliant registration/discovery endpoint ``` # Knowledge Graph * **Lifecycle Step**: [1 Discover](/category/discover/index.md) * **Pairs with**: [Agent2Agent Protocol (A2A)](/okf/protocols/a2a.md), [Model Context Protocol](/okf/protocols/mcp.md), [Agent Name Service v2 (ANS)](/okf/protocols/ans.md), [DNS-AID (DNS for AI Discovery)](/okf/protocols/dns-aid.md), [Agentic Resource Discovery (ARD)](/okf/protocols/ard.md), [A Framework for Agent Discovery in DAWN](/okf/protocols/dawn-agent-discovery-framework.md) [^ref-1]: draft-pioli-agent-discovery-00 (February 2026) specifies ARDP, a lightweight protocol providing stable agent identities (AIDs), dynamic endpoint resolution via RESOLVE/QUERY operations, capability advertisement across MCP/A2A/HTTP/gRPC, TTL-bounded presence records, and a minimal /.well-known/ardp/meta resource; a successor revision, draft-pioli-agent-discovery-01, was posted on 2026-02-24 and expired on 2026-08-28. (https://datatracker.ietf.org/doc/html/draft-pioli-agent-discovery-00) [^ref-2]: IETF Datatracker's status page for draft-pioli-agent-discovery (fetched 2026-09-06, distinct page from the htmlized draft text) shows the document's IESG state as "Expired", type "Expired Internet-Draft (individual) -- Expired & archived", with a single author (Roberto Pioli) whose listed e-mail "may no longer be valid", and only one revision beyond -00 (the -01 text, latest revision dated 2026-02-24) -- independently confirming this is a lapsed, unrenewed single-author submission rather than an active track. (https://datatracker.ietf.org/doc/draft-pioli-agent-discovery/) [^ref-3]: Expired Internet-Draft (expired 2026-08-28) (https://datatracker.ietf.org/doc/draft-pioli-agent-discovery/)