Glossary · Network and discovery
Agent discovery
How a client agent finds a remote agent and learns how to call it. A2A defines three routes: a well-known URI, registries and direct configuration.
Agent discovery is the process by which a client agent finds a remote agent that can handle a job and retrieves what it needs to call that agent.
What discovery returns. In A2A the result is an Agent Card: the agent’s name and provider, its skills and optional capabilities, the security schemes it accepts, and supportedInterfaces entries giving each endpoint URL, protocol binding and protocol version.
Three routes in A2A. Section 8.2 of the specification and the A2A Agent Discovery guide describe:
| Route | How it works | Suits |
|---|---|---|
| Well-known URI | GET https://{domain}/.well-known/agent-card.json |
Public agents, when the client already knows the domain |
| Registries and catalogs | Query a curated service by skill, tag, provider name or capability | Enterprises and marketplaces |
| Direct configuration | Hard-coded URLs, configuration files, environment variables or proprietary APIs | Known partners and development |
The guide notes that A2A does not prescribe a standard API for curated registries, and lists standardizing registry interactions as a future consideration.
The starting-point problem. The well-known URI route works once the client has a domain. A person’s agent often starts with something else: a phone number printed on a bill, a brand name, a support email address. Turning those into a domain, and knowing the answer really belongs to the business, takes a lookup outside A2A. Emissar’s Resolve module is aimed at that step, mapping phone numbers, domains and brand names to verified agent endpoints. Status: In development.
Discovery and trust. Finding a card tells a client where to send requests. Whether to trust the agent is a separate decision based on the TLS certificate of the serving domain, any card signatures, and the client’s own knowledge of the provider. The discovery guide also recommends access controls, such as mutual TLS or OAuth, on card endpoints when a card contains sensitive details, or serving those details in an authenticated extended Agent Card.
Neighbouring terms. An agent registry is a store of cards a client can query. Capability matching is the step of choosing among the agents discovery returns.