# ARD: 355 websites tell agents what resources they expose

Home > Standards > ARD (Agentic Resource Discovery)

## What is ARD?

**Agentic Resource Discovery is a proposed standard, published 26 Aug 2026 as v0.91 by authors at Google, Microsoft and Hugging Face, that lets a website list the resources it exposes to agents and, for each, two to five example questions it answers.** A site publishes it by any of three mechanisms: a JSON file at `/.well-known/ard.json` with an `entries` array, an `Agentmap:` directive in robots.txt pointing at an entries file, or a `<link rel="ard">` in the page head, with `rel="ai-catalog"` kept as the predecessor for compatibility. Each entry carries an identifier, a name, a media type, a URL or inline data, and the `representativeQueries` field.

## How does Known Good check it?

**From what the probe already holds.** Every probe stores the site's robots.txt and the head of its homepage, so the count reads the `Agentmap:` directive and the link relations from storage, and records whether either points at `/.well-known/ard.json`.

## How many websites publish ARD?

| Measured on 28 Sep 2026 | Sites |
| --- | --- |
| Any ARD mechanism | 355 |
| [`/.well-known/ard.json` referenced](https://knowngood.sh/standard/ard.md) | 111 |
| [`Agentmap:` directive in robots.txt](https://knowngood.sh/standard/ard.md) | 241 |
| [`<link rel="ard">` in the page head](https://knowngood.sh/standard/ard.md) | 90 |
| `rel="ai-catalog"` only (predecessor) | 172 |
| Could not ask (the consent check before any probe) | 2,382 |

This is the first measured count of ARD adoption we know of; the standard is 4 weeks old on the measurement date.

## Does ARD make a site agent-ready?

**ARD tells an agent what to ask; it does not answer the question.** A declaration is not one of the signals a listing counts. A site whose ARD entries point at resources that answer (a markdown page, an API, a server) is listed for those; the ARD file is the map.

## One implementation note

At least one widely used readiness scanner checks the predecessor `rel="ai-catalog"` and not the current `rel="ard"`. Serve all three mechanisms and both link relations; knowngood.sh does, at `/.well-known/ard.json` and `/.well-known/ai-catalog.json`.

## How do I add ARD to my site?

Publish `/.well-known/ard.json` with an `entries` array, add `Agentmap:` to robots.txt pointing at it, and put `<link rel="ard">` in your page head. Write two to five `representativeQueries` per entry in your own words: that field is a site telling an agent what to ask it. Then ask for a probe at [/submit](/submit).

## Frequently asked

**Is ARD an API?** No. It is a discovery file; the resources it lists are what an agent calls.

**Which mechanism should I use?** All three; they cost nothing and different agents read different ones.

Counts are of sites (hostnames), measured by Known Good's probe on 28 Sep 2026. Could-not-ask is counted beside the total, never inside it. Method: [/bot](/bot). Rubric: [/benchmark](/benchmark).

All standards: https://knowngood.sh/standards