The Agent Card: Discovery

A business card for an agent

An Agent Card is a JSON document in which a remote agent describes itself: name and description, version, the URL/endpoint where it accepts requests, supported capabilities (such as streaming and push notifications), accepted input and output modes, the skills it offers (each with an id, name and description, sometimes examples) and the authentication schemes a client must use. It is typically published at a well-known URL on the agent's domain (the exact path has varied by spec version, so check the current one) so clients can fetch and read it. Client agents, or the humans who configure them, use cards to decide whether and how to delegate. Treat card contents as untrusted input: descriptions are text a model may read, and an unverified card can lie about its skills.

An example Agent Card, checked

I ran this with plain Python 3 (standard library only). This card is an illustrative sample whose field names follow the general shape of A2A cards; the exact schema depends on the spec version. The script checks that required fields are present and reads the skills and authentication.

import json

card = {
    "name": "Refund Agent",
    "description": "Looks up invoices and proposes refunds. Cannot issue payments.",
    "url": "https://agents.example.com/refunds",
    "version": "1.2.0",
    "capabilities": {"streaming": True},
    "skills": [{"id": "propose-refund", "name": "Propose refund",
                "description": "Check an invoice and propose a refund amount."}],
    "authentication": {"schemes": ["bearer"]},
}
REQUIRED = ["name", "description", "url", "version", "skills"]
missing = [k for k in REQUIRED if k not in card]
print("missing fields:", missing)
print("skills:", [s["id"] for s in card["skills"]])
print("needs auth:", bool(card["authentication"]["schemes"]))
print(json.dumps(card)[:80] + "...")

Output:

missing fields: []
skills: ['propose-refund']
needs auth: True
{"name": "Refund Agent", "description": "Looks up invoices and proposes refunds....

Quick check: Why treat an Agent Card as untrusted?

• It cannot contain text
• It is always encrypted
• It is signed by the model
• It can misstate skills and contains text a model may read