# ardregistry.net > An independent reference for the Agentic Resource Discovery (ARD) specification: > what the format requires, how to publish a manifest, and measured adoption data. > Current to ARD v0.91 (Proposal, 2026-08-26). The manifest path is /.well-known/ard.json. The predecessor path /.well-known/ai-catalog.json was superseded in v0.91 on 2026-08-26. ## Pages - [Agentic Resource Discovery, explained properly](https://ardregistry.net/): What Agentic Resource Discovery (ARD) is, how the ard.json manifest works, and how agents find tools, skills and MCP servers at runtime. Current to spec v0.91 (26 Aug 2026), with live adoption data from 14,700 indexed resources. - [Get started with ARD](https://ardregistry.net/get-started/): The shortest path from nothing to an ARD manifest a registry can find: the file to copy, how to write representativeQueries that actually match, where the file goes, and how to check it worked. - [Publishing an ARD manifest](https://ardregistry.net/publish/): How to serve /.well-known/ard.json from nginx, Apache, Vercel, Netlify, GitHub Pages, Next.js, FastAPI, Express, Django and WordPress, plus the link tag, Agentmap and DNS alternatives. - [Building an ARD client](https://ardregistry.net/client/): How an agent discovers capabilities at runtime through ARD: the one required endpoint, a complete client in fifteen lines, how filters and federation work, and what the relevance score does not mean. - [The ARD specification, explained](https://ardregistry.net/spec/): A walkthrough of Agentic Resource Discovery v0.91 (2026-08-26): the design principles, the entry model, the five publishing mechanisms, the search API and federation, with the normative language quoted. - [ARD specification changelog](https://ardregistry.net/changelog/): What changed between ARD revisions: the August 2026 rename of ai-catalog.json to ard.json, the move to JSON-LD entries, query contexts, and what the working group has flagged as still unsettled. - [About this site](https://ardregistry.net/about/): Who runs ardregistry.net, why an independent ARD reference exists, how the measured figures are produced, and the conflict of interest declared up front. - [The ard.json manifest, field by field](https://ardregistry.net/ard-json/): Complete reference for the ard.json manifest: required and optional fields, the urn:air identifier format, working examples for MCP servers, skills, APIs and agents, and the ten mistakes that stop a manifest being indexed. - [ARD glossary](https://ardregistry.net/glossary/): Definitions for 41 terms in the Agentic Resource Discovery specification: ard.json, ARD entry, registry, federation, representativeQueries, trust manifest, urn:air identifiers and the rest, current to v0.91. - [Questions about Agentic Resource Discovery](https://ardregistry.net/faq/): 44 answers about the ARD specification: what it is, how to publish an ard.json manifest, how it differs from MCP, A2A and llms.txt, how federation and trust work, and why a valid manifest can still be invisible. - [ARD vs MCP](https://ardregistry.net/ard-vs-mcp/): ARD finds tools, MCP calls them. A side-by-side of Agentic Resource Discovery and Model Context Protocol: what each layer does, why they are not alternatives, and what to do if you already run an MCP server. - [ARD vs A2A](https://ardregistry.net/ard-vs-a2a/): A2A is how two agents talk. ARD is how one finds the other in the first place. How Agent Cards appear as ARD entries, what the url field must point at, and how many A2A agents are actually published. - [ARD vs llms.txt](https://ardregistry.net/ard-vs-llms-txt/): llms.txt suggests what an LLM should read. ARD describes what an agent can call, and has working consumers. What the published evidence says about whether llms.txt does anything, and why the two are not comparable. - [Moving from ai-catalog.json to ard.json](https://ardregistry.net/ai-catalog-json/): ARD v0.91 replaced /.well-known/ai-catalog.json with /.well-known/ard.json and rel=ai-catalog with rel=ard on 26 August 2026. What changed, why most documentation still shows the old name, and the three-step migration. - [State of ARD](https://ardregistry.net/state-of-ard/): Measured ARD adoption as of 4 September 2026: 14,732 resources from 6,610 publishers, 97,230 tools, what happens when you actually call the endpoints, and the full method. - [ARD registries, compared](https://ardregistry.net/registries/): A conformance probe of every public Agentic Resource Discovery registry: which serve POST /search at the spec path, which support /explore and /agents, which publish their own manifest, and which return 404 where 405 is correct. - [Check an ARD manifest](https://ardregistry.net/validate/): Free validator for ard.json manifests. Give a domain or paste JSON and get the errors, the warnings, and the full list of checks against ARD v0.91. Nothing is stored. - [Who has published an ARD manifest](https://ardregistry.net/publishers/): Measured ARD adoption: 206 domains serve a manifest out of 375,997 crawled, and 85% of them are still on the predecessor path superseded in August 2026. Who they are and what they publish. ## Machine readable - [ARD manifest](https://ardregistry.net/.well-known/ard.json) - [Measured index snapshot](https://ardregistry.net/api/stats.json)