A2A Agent Card

What it checks

The extension looks for an Agent2Agent (A2A) agent card at these paths, in order:

1. /.well-known/agent-card.json
2. /.well-known/agent.json (the earlier A2A path, kept as a fallback)

The first path that returns a successful, non-empty JSON response is parsed. The check is deliberately loose: it confirms the document is an agent card and says what the agent can do. That means a non-empty name, plus either a non-empty skills array or a capabilities field. It does not validate the rest of the A2A schema.

If neither path serves a card, the extension follows a pointer the site publishes to an agent card hosted elsewhere: an entry in its agent catalog (/.well-known/ard.json or /.well-known/ai-catalog.json), or a DNS-AID record. It never guesses a hostname, it does not follow redirects from the declared address, and it never requests an address on your local network unless the site being audited is on it too.

Results

Status	When
Pass	A card with a name and either skills or capabilities was found
Pass	A host the site declares serves an agent card
Warn	A card was found but is not valid JSON
Warn	A card was found but has no name, or neither skills nor capabilities
N/A	No agent card was found at either path

How to fix

If you run an agent that other agents can call, publish its card at /.well-known/agent-card.json. Give it a name, the endpoint, and a list of skills:

{
  "name": "Example support agent",
  "description": "Answers questions about orders and returns.",
  "version": "1.0.0",
  "supportedInterfaces": [
    { "url": "https://example.com/a2a", "protocolBinding": "JSONRPC", "protocolVersion": "1.0" }
  ],
  "capabilities": {},
  "defaultInputModes": ["text/plain"],
  "defaultOutputModes": ["text/plain"],
  "skills": [
    {
      "id": "order-status",
      "name": "Order status",
      "description": "Reports the status of an order.",
      "tags": ["orders"]
    }
  ]
}

If your card is at /.well-known/agent.json, it still passes, but the current path is /.well-known/agent-card.json.

Related: Agent Skills.

Support by agent and browser

Announced means the vendor’s own docs or announcement say so. Published is the date on the vendor’s own page, where it has one. Checked is the last time our weekly research found that page still saying so.

Agent	Status	Source
AI assistants
Gemini Google	Partial support	partial Register and manage A2A agents (Gemini Enterprise docs) Published 8 Oct 2026 · Checked 9 Oct 2026This is Gemini Enterprise (Preview), not the consumer Gemini app. Admins paste the agent card JSON in. The card is not fetched from /.well-known.
Copilot Microsoft	Partial support	partial Connect to an agent over the Agent2Agent (A2A) protocol - Microsoft Copilot Studio Published 26 Aug 2026 · Checked 9 Oct 2026This is Copilot Studio (the Microsoft 365 Copilot agent builder), not consumer Copilot. It needs an admin-entered A2A endpoint; 'if your agent has a valid agent card on the standard .well-known URL, Copilot Studio automatically pulls the name and description'. The docs reference endpoint + /.well-known/agent.json.

No evidence yet25

• ChatGPT
• Claude
• Perplexity
• Meta AI
• ChatGPT Atlas
• Comet
• Dia
• Gemini in Chrome
• Edge Copilot Mode
• Claude Code
• Cursor
• Codex
• GitHub Copilot
• Windsurf
• CCBot
• Applebot
• Amazonbot
• Bytespider
• Cohere
• Mistral
• DuckAssist
• Chrome
• Edge
• Firefox
• Safari

Names and marks belong to their owners and are used only to identify products. None of these vendors is affiliated with Sitebulb. Spotted something out of date? Send a correction.

Adoption on the top 100 sites

1%

1 of 91 measured sites implement it

Scanned 23 Oct 2026 with the Sitebulb Labs extension, against the Tranco list (tranco-56Z8N). 9 sites couldn’t be measured (bot challenge or timeout) and are left out of the share.

Sites implementing it1

1. #2 cloudflare.com

Overview

2/9

Speculative

Specified, but little evidence anything uses it yet.

How this rating is worked out2 of 9 points

Factor	Points	Why
Vendor support	1 / 3	0 vendors supporting, 2 partly or planned
Top-100 adoption	1 / 3	1% of measured sites
Spec maturity	0 / 3	Community proposal

8 or more points is Established, 5 to 7 is Gaining traction, 2 to 4 is Speculative and under 2 is Stalled. A feature is also Stalled when more vendors have said no than yes. Read the spec.

Community insights

No community insights for this feature yet.

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