agenticweb.wiki

Agentic Resource Discovery (ARD)

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This page is about Agentic Resource Discovery (ARD), the open specification from the ards-project that publishes agentic resources (MCP servers, A2A agents, skills, registries) at /.well-known/ard.json and makes them searchable through registries. It is not RFC 9727 (/.well-known/api-catalog), the IETF standard for listing APIs, and not the AI Catalog well-known file (/.well-known/ai-catalog.json), the separate AI Catalog format whose path ARD used before v0.91. It is also not ARDP, the unrelated IETF draft "Agent Registration and Discovery Protocol" [18]. ERC-8444 [20] and draft-hood-agtp-ard [19] are third-party extensions that build on ARD, not ARD itself.

Overview

ARD lets an organisation describe its agentic resources (MCP servers, A2A agents, skills, APIs, other catalogs and registries) once, on its own domain, in a manifest at /.well-known/ard.json, so that agents can find them by search instead of having each one installed in advance [1][11]. Registries crawl these manifests, index each entry (including the sample user queries an entry SHOULD carry), and answer natural-language search requests over a required HTTP REST API; the agent then connects to the chosen resource through its own protocol [1][13]. ARD is an envelope, not a replacement for the formats it points to: an MCP Server Card, an A2A Agent Card or an OpenAPI file stays defined by its own spec, and the entry only names its media type [1][10]. ARD first used the AI Catalog’s /.well-known/ai-catalog.json path; since v0.91 it has its own path and entry model, kept compatible with AI Catalog, and RFC 9727’s /.well-known/api-catalog remains a separate IETF standard for listing APIs [1][3][8][10].

Who uses it

Each URL below returned HTTP 200 with no redirect on 2026-10-28, with the content-type shown, and a JSON body with a top-level "entries" array. "First entry" gives the identifier, type and url of the first item in that array. These five are examples, not a complete list: more sites served the file when checked the same day. Some large publishers, such as GitHub and Hugging Face, served only the predecessor /.well-known/ai-catalog.json and not /.well-known/ard.json on 2026-10-28.

Who reads it

Lighthouse checks the catalog of the site being audited [16][23]. The other statements describe search over registries and curated catalogs. No vendor statement found, as of 2026-10-28, naming a production crawler that fetches /.well-known/ard.json across the open web.

Recent coverage

See also

References

  1. Junjie Bu (Google), R.V. Guha and Shaun Smith (Hugging Face), Agentic Resource Discovery Specification, v0.91, "Proposal", August 26, 2026 (rendered from spec/ard.md): "Version: v0.91 Status: Proposal Date: August 26, 2026" "Authors: Junjie Bu — Google R.V.Guha Shaun Smith — Hugging Face" "The Agentic Resource Discovery Specification (ARD) defines how agentic resources are described, discovered, and searched across federated networks." "Well-Known URI: Hosting a manifest of entries at https://{domain}/.well-known/ard.json." "The manifest is a JSON document with an entries array of ARD entries (§4); any other top-level members are transport-defined and ignored by ARD." "A consumer resolving a domain’s entries MUST fetch /.well-known/ard.json, and MUST honour a rel="ard" link." "ARD’s predecessor specified the path /.well-known/ai-catalog.json and the link relation ai-catalog; a consumer MAY additionally consult these, and a consumer that does treats them as equivalent entry sources." "A resource that remains only at /.well-known/ai-catalog.json may not be found, since consulting that path is optional for consumers — a publisher on the predecessor path SHOULD move to ard.json." "An entry is a JSON-LD node describing an agentic resource." "Agentmap Directive: Adding an entry-source directive in robots.txt (e.g. Agentmap: https://example.com/entries.json)." "HTML Link Tag: Including <link rel="ard" href="..."> in the <head> of a document." "DNS: Publishing Service Binding records that point to either a static entry source (e.g. _entries._agents.example.com) or a dynamic Agent Registry search endpoint (e.g. _search._agents.example.com)." "An Agent Registry MUST expose a standard HTTP REST search interface to guarantee universal federation." "The specification does not define or constrain the internal schema of specific agent types (MCP, A2A, etc.). Instead, it acts as a clean envelope that uses a type term (formatted as an RFC 6838 / IANA Media Type) to identify what an artifact is, delegating the definition of artifact-specific metadata to the respective protocol specifications." "application/mcp-server-card+json — MCP Server Card" "are de-facto community standards tracking towards formal registration." — https://agenticresourcediscovery.org/spec/
  2. ards-project, ard-spec GitHub repository README (Apache-2.0), checked 2026-10-28; quoted from the raw README: "Canonical home of the Agentic Resource Discovery specification — a federated, domain-anchored standard for cataloging, searching, and discovering agentic resources (MCP servers, A2A agent cards, Skills, APIs, and other callable services) across networks of discovery services." "the docs site renders spec/ard.md directly from this repo, so this is the single source of truth." "spec/ard-v0.9.md — the previous version, kept reachable" — https://github.com/ards-project/ard-spec
  3. ards-project, Agentic Resource Discovery Specification v0.9 (Draft), dated May 28, 2026, kept in the repository as spec/ard-v0.9.md; quoted from the raw file: "Version: v0.9 (Draft) Status: Proposal Date: May 28, 2026" "A manifest file hosted at /.well-known/ai-catalog.json lists the available artifacts." — https://github.com/ards-project/ard-spec/blob/main/spec/ard-v0.9.md
  4. ards-project, commit 33be466, 2026-06-12 02:10 UTC (text checked through the GitHub API): "Rebrand Agent Finder -> Agentic Resource Discovery (ARD) across the repo" — https://github.com/ards-project/ard-spec/commit/33be46675231fec2939626b09bc438d3ae1616e3
  5. ards-project, commit c61d233, 2026-06-16 16:35 UTC (text checked through the GitHub API): "bump version to v0.9 (Draft)" — https://github.com/ards-project/ard-spec/commit/c61d233614c9380671d4c055f3e5de6e316ab781
  6. ards-project, commit a305a52, 2026-08-26 18:01 UTC (text checked through the GitHub API): "spec: publish v0.91 — promote the draft, single well-known path" — https://github.com/ards-project/ard-spec/commit/a305a5285ed6df33f467c67d1f7a9ab672530fcb
  7. ards-project, commit b76db39, 2026-08-26 18:55 UTC (text checked through the GitHub API): "spec: remove R.V.Guha’s affiliation from the author list" — https://github.com/ards-project/ard-spec/commit/b76db39bcdca0ef826d48ae407b61a81f4605cb1
  8. ards-project, ADR 0010: Loose Coupling Between ARD Entries and AI Catalog Entries, decision dated 2026-07-09; quoted from the raw file: "Status: Accepted Date: 2026-07-09" "An ARD entry is the ai-catalog core plus flat, namespaced extensions." "So the two pull in opposite directions." — https://github.com/ards-project/ard-spec/blob/main/adr/0010-ard-and-ai-catalog-loose-coupling.md
  9. AgenticResourceDiscovery.org, Governance page, checked 2026-10-28: "ARD is governed by a deliberately lightweight structure with four commitments: direction stays with organizations actually shipping ARD, technical control stays with people chosen for expertise, no single company can capture the specification, and participation is never bought." "Specification changes are agreed by majority vote of the Maintainers." "R.V. Guha (Chair) Member at large" — https://agenticresourcediscovery.org/governance/
  10. AgenticResourceDiscovery.org, Interoperability page, checked 2026-10-28: "ARD defines its own entry and its own manifest at /.well-known/ard.json." "The relationship is compatibility, not dependency." "when a publisher serves both ard.json and ai-catalog.json with entries that share an identifier, the ard.json entry takes precedence for ARD discovery." — https://agenticresourcediscovery.org/interoperability/
  11. Junjie Bu and Srinivas Krishnan, Google, Announcing the Agentic Resource Discovery specification (Google Developers Blog), 2026-06-17: "That’s why we’re announcing Agentic Resource Discovery (ARD), an open specification for publishing, discovering, and verifying AI capabilities across the web." "Publishing the catalog: The provider hosts an ai-catalog.json file at a well-known path on its domain." "The Agentic Resource Discovery specification is licensed under Apache 2.0 and is built upon the foundational AI Catalog data model." "We are grateful to the AI Catalog Working Group under the Linux Foundation, as well as the launch partners who helped shape the specification and reference implementations." "Native support for ARD will be available in Agent Platform in the coming months, allowing organizations to securely connect their internal registries to the broader network." — https://developers.googleblog.com/en/announcing-the-agentic-resource-discovery-specification/
  12. Ramanathan Guha, Microsoft, Introducing the Agentic Resource Discovery specification (Microsoft Command Line), 2026-06-17: "By Ramanathan Guha Technical Fellow, Microsoft 2026.06.17" "Microsoft is developing ARD in collaboration with Cisco, Databricks, GitHub, GoDaddy, Google, Hugging Face, Nvidia, Salesforce, ServiceNow, and Snowflake." "Built on ARD, GitHub’s agent finder gives developers and enterprises control over what AI resources their agents use while simultaneously preventing unneeded resources from bloating the context window." "Instead of pre-loading everything, agent finder searches GitHub’s curated catalog of public AI resources or your own private registry, and Copilot finds which resources the prompt calls for and injects them into the context window when you need them." — https://commandline.microsoft.com/agentic-resource-discovery-specification-ard/
  13. Ben Burtenshaw and Shaun Smith, Hugging Face, Agentic Resource Discovery: Let agents search for tools, skills, and other agents (Hugging Face blog), 2026-06-17: "The Hugging Face Discover Tool is our reference implementation of ARD." "It provides search access to thousands of Skills, ML applications, and MCP Servers — on Hugging Face and across other ARD discovery services." — https://huggingface.co/blog/agentic-resource-discovery-launch
  14. AI Catalog working group (Agent-Card/ai-catalog), AI Catalog specification source (specification/ai-catalog.md), checked 2026-10-28; quoted from the raw file: "To support automated discovery, hosts MAY serve an AI Catalog at the following well-known URI [[RFC8615]]: /.well-known/ai-catalog.json" "An AI Catalog document is identified by the media type: application/ai-catalog+json" — https://github.com/Agent-Card/ai-catalog/blob/main/specification/ai-catalog.md
  15. Agent-Card/ai-catalog GitHub repository README, checked 2026-10-28; quoted from the raw README: "Members from various AI protocols (MCP, A2A, and others) are collaborating on a common AI Catalog standard for discovering heterogeneous AI artifacts across the ecosystem." — https://github.com/Agent-Card/ai-catalog
  16. GoogleChrome/lighthouse, pull request #17168 new_audit(ard-schema): add Agent Resource Discovery audit, opened 2026-08-10, merged 2026-08-31 (text checked through the GitHub API): "Adds the Agentic Resource Discovery (ARD) schema conformance audit (ard-schema) to Lighthouse under the agentic-browsing category." — https://github.com/GoogleChrome/lighthouse/pull/17168
  17. GoogleChrome/lighthouse, release v13.5.0, published 2026-09-18 (text checked through the GitHub API): "ard-schema: add Agent Resource Discovery audit" — https://github.com/GoogleChrome/lighthouse/releases/tag/v13.5.0
  18. R. Pioli, draft-pioli-agent-discovery-01, Agent Registration and Discovery Protocol (ARDP), individual Internet-Draft, February 2026, now expired: "Published: February 2026" "This document specifies the Agent Registration and Discovery Protocol (ARDP), a lightweight protocol for registering, discovering, and reaching autonomous software agents in distributed and federated environments." — https://datatracker.ietf.org/doc/html/draft-pioli-agent-discovery
  19. C. Hood (Nomotic, Inc.), draft-hood-agtp-ard-00, ARD Binding for AGTP, individual Internet-Draft, 18 June 2026: "Published: 18 June 2026 Intended Status: Informational" "The Agentic Resource Discovery (ARD) specification defines a federated, domain-anchored model for cataloging, discovering, and searching agentic resources across organizational boundaries." — https://datatracker.ietf.org/doc/html/draft-hood-agtp-ard
  20. Gary Yang, ERC-8444: Agentic Resource Discovery (ARD) Onchain (Ethereum Improvement Proposals, Draft), created 2026-10-12: "Created 2026-10-12" "This ERC defines an onchain registry of value records for agentic resources." — https://eips.ethereum.org/EIPS/eip-8444
  21. Matt G. Southern, Google, Microsoft Back Draft AI Agent Discovery Spec (Search Engine Journal), 2026-06-18: "ARD moves discovery into a search step that happens at runtime." — https://www.searchenginejournal.com/google-microsoft-back-draft-ai-agent-discovery-spec/579894/
  22. Manuel Masiero, Agentic Resource Discovery: Search engine for AI agents (heise online), 2026-06-19: "ARD enables AI agents to automatically find suitable tools at runtime." — https://www.heise.de/en/news/Agentic-Resource-Discovery-Search-engine-for-AI-agents-11338833.html
  23. Matt G. Southern, Google Lighthouse Adds Audit For AI Agent Resource Discovery (Search Engine Journal), 2026-09-21: "If the site does not provide a catalog pointer, Lighthouse defaults to /.well-known/ai-catalog.json." "The most recent spec, dated Aug. 26, moved this file to ard.json, with the old filename remaining optional for software that reads it." — https://www.searchenginejournal.com/google-lighthouse-ai-agent-resource-discovery-audit/590274/
  24. IANA, Well-Known URIs registry, checked 2026-10-28: no row for ard.json or ai-catalog.json (checked against the registry’s CSV export; the Link Relations CSV likewise has no "ard" or "ai-catalog" row) — https://www.iana.org/assignments/well-known-uris

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