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The key difference in an A2A Agent Card is its protocol version: v0.3 puts the endpoint in top-level url and protocolVersion fields, while v1.0 puts endpoint details in an ordered supportedInterfaces array. Cloud services may expose only part of the protocol schema or impose additional transport and access requirements, so compare the card version and the provider’s implementation separately.
What fields are in an A2A Agent Card?
The A2A protocol defines the card; its fields describe an agent, how to reach it, what it can do, and how clients should interact with it. The schema differs by protocol version. A cloud API may also define a narrower resource representation, which should not be mistaken for the complete protocol card.
| Field group | A2A v1.0 | v0.3 or implementation note |
|---|---|---|
| Identity | name, description, and agent version. |
v0.3 also includes these. The agent’s version is distinct from the A2A protocol version. |
| Endpoint and binding | Ordered supportedInterfaces[]; each interface identifies a url, protocolBinding, and protocolVersion. The first interface is preferred. |
v0.3 uses top-level url and protocolVersion. The v1.0 schema deprecates the top-level protocol-version field. |
| Provider and documentation | Optional provider and documentationUrl. |
These are descriptive protocol metadata, not universal cloud endpoint fields. |
| Capabilities | capabilities can describe streaming, push notifications, extensions, and extended-card availability. |
Google’s v0.3 example also shows stateTransitionHistory; do not assume feature sets are identical across versions. |
| Security | Optional security scheme definitions and requirements. v1.0 includes API key, HTTP, OAuth 2.0, OpenID Connect, and mutual TLS scheme types. | The card describes authentication requirements, but actual endpoint access remains subject to the cloud service’s rules. Do not put secrets in a public card. |
| Input and output modes | defaultInputModes and defaultOutputModes. |
Skills can specify more precise modes; Google’s documentation includes MIME-type examples. |
| Skills | skills[] entries include id, name, description, and tags; examples can describe useful request patterns. |
Google’s trimmed CX API representation requires core card fields and exposes per-skill input and output modes. |
| Integrity and discovery | Cards can include JWS signatures. The current specification standardizes discovery at /.well-known/agent-card.json. |
Confirm that a target implementation supports the URI and signature behavior. Microsoft Foundry uses version-specific card URLs and requires Entra authentication. |
The A2A specification explains that an AgentInterface “allows agents to expose the same functionality over multiple protocol binding mechanisms.” That flexibility is why an interface’s URL, binding, and protocol version need to be read together. A2A Protocol Specification
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsWhat changes between A2A Agent Card v0.3 and v1.0?
The central structural change is endpoint placement. In v0.3, a card has one top-level endpoint URL and protocol version. In v1.0, each entry in supportedInterfaces pairs an endpoint URL with its binding and protocol version, and array order indicates preference. A v0.3 card should therefore be validated against the v0.3 schema, not mechanically treated as a v1.0 card with renamed fields.
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Google Cloud Agent Registry documents both versions and recommends v1.0. Its v0.3 reference limits protocolVersion to 0.3 or a 0.3 patch such as 0.3.1, because v1.0 deprecates that top-level field. The Agent Registry specification file has a 10 KB maximum. Google Cloud Agent Registry Agent Card reference
How do Google Cloud, Microsoft Foundry and AWS AgentCore represent cards?
Cloud documentation describes service-specific behavior as well as card fields. These representations and restrictions should be distinguished from the normative A2A schema.
Google Cloud
Google Cloud Agent Registry supports Agent Card v0.3 and v1.0, with v1.0 recommended. Gemini Enterprise registration accepts a JSON Agent Card and can use optional authorization configuration to access Google Cloud resources on a user’s behalf. That authorization configuration is a registration mechanism, not a protocol-card field. Google Cloud Agent Registry Agent Card reference
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Microsoft Foundry
Microsoft documents A2A v1.0 as generally available and v0.3 as preview. It provides separate card endpoints for each version and projects authored content into both shapes. Its documented inbound transport matrix lists HTTP+JSON and JSON-RPC for v0.3, and JSON-RPC only for v1.0; gRPC is not listed as supported. Microsoft also requires Microsoft Entra ID authentication for A2A URLs and does not support anonymous card access. Microsoft Foundry incoming A2A documentation
AWS Bedrock AgentCore
The AWS Bedrock AgentCore Developer Guide states that an agent card’s capabilities, skills, and communication interface are validated against the A2A Agent Card specification. That statement supports a validation claim; it does not establish a separate AWS field schema, protocol-version matrix, or transport behavior. AWS Bedrock AgentCore Developer Guide
Quick Recap
How to compare two Agent Cards
- Identify the protocol version. Validate each card against the schema for that version before comparing field values. Google documents both v0.3 and v1.0 structures in its Agent Registry reference.
- Compare endpoint definitions and preference. For v1.0, inspect each interface’s URL, binding, and protocol version, preserving array order. For v0.3, inspect the top-level endpoint fields.
- Check capability and mode compatibility. Compare declared capabilities and input/output modes with what the deployed service actually supports. A capability advertised in a card does not override provider transport limits, as Microsoft’s documented version-specific matrix illustrates.
- Review skills as discovery metadata. Compare each skill’s identifier, description, tags, examples, and modes. These descriptions help a client discover intended uses; they do not prove that a request will execute successfully.
- Check security declarations and access independently. Compare card security schemes with the service’s actual access-control requirements. Microsoft’s authenticated card URLs show that discovery itself may require credentials, separate from authentication for agent calls.
- Separate protocol fields from cloud wrappers. For example, Google registration’s
authorizationConfigand the CX API’s trimmed REST resource are service-level concepts, not additions to the universal A2A card schema.
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