Side by side
All twelve on one screen
Grouped by the job each one does for an AI agent. Pick a name for the full story.
| Standard | Job in one phrase | When to use it | Who's behind it | Status |
|---|---|---|---|---|
| ARD | Search for agent tools across the web | When you offer APIs, MCP servers or agents and want agent search registries to find them. | Google-led authors (Google, Hugging Face, R.V. Guha) | Early usev0.91 "Proposal" (Aug 26, 2026); small real use |
| ai-catalog | A site's list of its AI offerings | When you publish that same list for MCP Server Cards and older tools. Serve one file at both addresses. | Linux Foundation working group (MCP and A2A communities) | Early useDraft; MCP Server Cards point to it; small real use |
| WebMCP | A page hands typed tools to the agent in your browser | When agents use your site in people's browsers. Add tools to your key flows and keep the normal page. | W3C Web ML community group; Microsoft and Google editors | Early useDraft (Oct 9, 2026); Chrome and Edge trials; live in ChatGPT desktop and Shopify |
| NLWeb | Ask a website questions in plain language | When you have lots of structured content and want people and agents to query it. | Microsoft (R.V. Guha) | Early useSpec v0.55; W3C group without chairs; no deployment count |
| Web Bot Auth | Cryptographic ID for bots | When your bot visits other sites and must prove it's really yours, or you verify bots on yours. | Cloudflare and Google authors, IETF working group | In productionWG draft -00 (Sept 1, 2026); live signers |
| Poppy | Your agent signs in to a company as you | When customers' own agents should sign in and act on their accounts. Track it; it's a fresh draft. | Sierra + Meta; 6 launch and 35 design partners | DraftDraft 0.1 (Oct 9, 2026); no known deployments |
| auth.md | Your agent signs you up for a new service | When you want agents to create accounts on your developer service without a sign-up form. | WorkOS (open, MIT) | Early usev0.6.0 (June 10, 2026); live at Neon, Cloudinary, monday.com, Firecrawl |
| UCP | A shared language for agent shopping | When you sell goods and want any AI assistant to browse, cart and check out. | Google + Shopify, with governing and tech councils | In productionv2026-08-25; widely deployed via Shopify |
| ACP | Products (and checkout) into ChatGPT | When you want your products shown in ChatGPT, especially if you already use Stripe. | OpenAI + Stripe | In productionBeta, stable 2026-04-17; live for discovery |
| AP2 | Signed proof of what you authorized | When an agent pays and you need proof a person approved those exact terms. Still early. | Google, now at the FIDO Alliance | Early usev0.2 (Apr 28, 2026); early standardization |
| MPP | Pay inside a web request, card or crypto | When agents pay per call or by the minute and you want cards and stablecoins via Stripe. | Stripe + Tempo | Early useIndividual IETF draft -01 (Sept 9, 2026); live on Tempo |
| x402 | Cents-per-request payments over HTTP 402 | When you charge per API request in stablecoins, with no accounts or sign-up. | Coinbase, now the x402 Foundation (Linux Foundation) | In productionV2 (Dec 11, 2025); foundation live; low real volume |
The ones people mix up
Same neighbourhood, different jobs.
ARD vs ai-catalog
Discovery vs. publishing. Serve both.
- ARD
The discovery format. Registries crawl it and answer searches.
- ai-catalog
The publishing format. Your site's list of its AI offerings.
- ARD
UCP vs ACP
Any assistant vs. ChatGPT.
MPP vs x402
Cards and stablecoins via Stripe vs. stablecoin payments per request under a neutral foundation.
Web Bot Auth vs auth.md vs Poppy
Which bot is this, sign up a new user, act for an existing customer.
- Web Bot Auth
Which bot is this?
- auth.md
Sign up a new user.
- Poppy
Act for an existing customer.
- Web Bot Auth