# Agentic Resource Discovery vs api-catalog: A Well-Known URI and Link Relation to Help Discovery of APIs

The map lists them as complementary: sites and agents commonly implement both.

[1 Discover](/category/discover/) [Agentic Resource Discovery](/protocols/ard/) · [1 Discover](/category/discover/) [api-catalog: A Well-Known URI and Link Relation to Help Discovery of APIs](/protocols/api-catalog-rfc9727/)

|  | [Agentic Resource Discovery](/protocols/ard/) ARD | [api-catalog: A Well-Known URI and Link Relation to Help Discovery of APIs](/protocols/api-catalog-rfc9727/) RFC 9727 |
| --- | --- | --- |
| Lifecycle step | 1 Discover: What is here, and where? | 1 Discover: What is here, and where? |
| Answers | Where are an organization's discoverable agentic resources (MCP servers, A2A agents, skills, registries), and how can they be found by search rather than pre-installed one at a time? | Given a publisher's domain, where is the machine-readable list of the APIs it exposes? |
| Governed by | Authored by individuals at Google, Microsoft and Hugging Face (Junjie Bu, R.V. Guha, Shaun Smith); published as an open GitHub project (ards-project/ard-spec) with no formal standards body yet; contributions acknowledged from AWS, Cisco, Databricks, GitHub, GoDaddy, Nvidia, Salesforce and Snowflake | IETF; published as a Standards Track RFC with the IETF as change controller |
| Status (issuer's words) | Proposal | Proposed Standard (errata exist) |
| Phase | draft | stable |
| Version | v0.91 (2026-08-26) | RFC 9727 (2025-06) |
| Form / transport | well-known file | well-known file |
| Found at | /.well-known/ard.json | /.well-known/api-catalog |
| Adoption | observed — agenticresources.dev own probe, 2026-09-04 | unmeasured |
| Evidence | 2 verified, 2 reported | 2 verified |
| Primary use case | Let agents discover my API or service | Let agents discover my API or service |
| Last verified | 2026-10-19 (current) | 2026-10-16 (current) |
| Specification | [https://raw.githubusercontent.com/ards-project/ard-spec/main/spec/ard.md](https://raw.githubusercontent.com/ards-project/ard-spec/main/spec/ard.md) | [https://www.rfc-editor.org/rfc/rfc9727.html](https://www.rfc-editor.org/rfc/rfc9727.html) |

## When to use which

- Choose Agentic Resource Discovery when your question is “Where are an organization's discoverable agentic resources (MCP servers, A2A agents, skills, registries), and how can they be found by search rather than pre-installed one at a time?” and you accept its maturity: phase draft, adoption observed (agenticresources.dev own probe, 2026-09-04).
- Choose api-catalog: A Well-Known URI and Link Relation to Help Discovery of APIs when your question is “Given a publisher's domain, where is the machine-readable list of the APIs it exposes?” and you accept its maturity: phase stable, adoption unmeasured.

Guidance is derived from the two records (question, phase, adoption, prerequisites, pairings), not from opinion. Each record's page carries its numbered references.

## Read the full articles

- [Agentic Resource Discovery](/protocols/ard/): Where are an organization's discoverable agentic resources (MCP servers, A2A agents, skills, registries), and how can they be found by search rather than pre-installed one at a time?
- [api-catalog: A Well-Known URI and Link Relation to Help Discovery of APIs](/protocols/api-catalog-rfc9727/): Given a publisher's domain, where is the machine-readable list of the APIs it exposes?

Ask the MCP server to compare any two: the compare-protocols prompt, or get on both ids. [Connect](/connect/).

[ard.json](/data/protocols/ard.json) · [api-catalog-rfc9727.json](/data/protocols/api-catalog-rfc9727.json) · [Markdown](/compare/ard-vs-api-catalog-rfc9727/index.md)