Design A2A Agent Card

Design A2A Agent Card

Create a standards-compliant A2A Agent Card that advertises an agent's identity, skills, authentication requirements, and capabilities for discovery by other agents.

When to Use

• Building an agent that must be discoverable by other A2A-compliant agents
• Exposing agent capabilities for multi-agent orchestration
• Migrating an existing agent to the A2A (Agent-to-Agent) protocol
• Defining the public contract for an agent before implementation
• Integrating with agent registries or directories that consume Agent Cards

Inputs

• Required: Agent name and description
• Required: List of skills the agent can perform (name, description, input/output schemas)
• Required: Base URL where the agent will be hosted
• Optional: Authentication method (none, oauth2, oidc, api-key)
• Optional: Supported content types beyond text/plain (e.g., image/png, application/json)
• Optional: Capability flags (streaming, push notifications, state transition history)
• Optional: Provider organization name and URL

Procedure

Step 1: Define Agent Identity and Description

1.1. Choose the agent identity fields:

{
  "name": "data-analysis-agent",
  "description": "Performs statistical analysis, data visualization, and report generation on tabular datasets.",
  "url": "https://agent.example.com",
  "provider": {
    "organization": "Example Corp",
    "url": "https://example.com"
  },
  "version": "1.0.0"
}

1.2. Write a clear, actionable description that answers:

• What domains does this agent cover?
• What kinds of tasks can it handle?
• What are its limitations?

1.3. Set the canonical URL where the Agent Card will be served at /.well-known/agent.json.

Expected: A complete identity block with name, description, URL, provider, and version.

On failure: If the agent serves multiple domains, consider whether it should be one agent with many skills or multiple agents with focused scopes. A2A favors focused agents with clear boundaries.

Step 2: Enumerate Skills with Input/Output Schemas

2.1. Define each skill the agent can perform:

{
  "skills": [
    {
      "id": "analyze-dataset",
      "name": "Analyze Dataset",
      "description": "Run descriptive statistics, correlation analysis, or hypothesis tests on a CSV dataset.",
      "tags": ["statistics", "data-analysis", "csv"],
      "examples": [
        "Analyze the correlation between columns A and B in my dataset",
        "Run a t-test comparing group 1 and group 2"
      ],
      "inputModes": ["text/plain", "application/json"],
      "outputModes": ["text/plain", "application/json", "image/png"]
    },
    {
      "id": "generate-chart",
      "name": "Generate Chart",
      "description": "Create bar, line, scatter, or histogram charts from tabular data.",
      "tags": ["visualization", "charts"],
      "examples": [
        "Create a scatter plot of height vs weight",
        "Generate a histogram of the age column"
      ],
      "inputModes": ["text/plain", "application/json"],
      "outputModes": ["image/png", "image/svg+xml"]
    }
  ]
}

2.2. For each skill, provide:

• id: Unique identifier (kebab-case)
• name: Human-readable display name
• description: What the skill does, in one to two sentences
• tags: Searchable keywords for discovery
• examples: Natural language task examples that trigger this skill
• inputModes: MIME types the skill accepts
• outputModes: MIME types the skill can produce

2.3. Ensure skill boundaries are clear and non-overlapping. Each task should map to exactly one skill.

Expected: A skills array where each entry has id, name, description, tags, examples, and I/O modes.

On failure: If skills overlap significantly, merge them into a single broader skill with more examples. If a skill is too broad, split it into focused sub-skills.

Step 3: Configure Authentication

3.1. Define the authentication scheme based on deployment context:

No authentication (local/trusted network):

{
  "authentication": {
    "schemes": []
  }
}

OAuth 2.0 (recommended for production):

{
  "authentication": {
    "schemes": ["oauth2"],
    "credentials": {
      "oauth2": {
        "authorizationUrl": "https://auth.example.com/authorize",
        "tokenUrl": "https://auth.example.com/token",
        "scopes": {
          "agent:invoke": "Invoke agent skills",
          "agent:read": "Read task status"
        }
      }
    }
  }
}

API Key (simple shared-secret):

{
  "authentication": {
    "schemes": ["apiKey"],
    "credentials": {
      "apiKey": {
        "headerName": "X-API-Key"
      }
    }
  }
}

3.2. Choose the minimum viable authentication for the deployment environment:

• Local development: none
• Internal services: apiKey
• Public-facing agents: oauth2 or oidc

3.3. Document the token/key provisioning process in the Agent Card's provider section or external documentation.

Expected: An authentication block matching the deployment security requirements.

On failure: If OAuth 2.0 infrastructure is not available, start with API key authentication and plan migration. Never deploy a public agent with none authentication.

Step 4: Specify Capabilities

4.1. Declare what protocol features the agent supports:

{
  "capabilities": {
    "streaming": true,
    "pushNotifications": false,
    "stateTransitionHistory": true
  }
}

4.2. Set each capability flag based on implementation readiness:

• streaming: true if the agent supports SSE streaming via tasks/sendSubscribe. Enables real-time progress updates for long-running tasks.
• pushNotifications: true if the agent can send webhook callbacks when task state changes. Requires the agent to store and call back webhook URLs.
• stateTransitionHistory: true if the agent maintains a full history of task state transitions (submitted, working, completed, etc.). Useful for audit trails.

4.3. Only set capabilities to true if the implementation fully supports them. Advertising unsupported capabilities breaks interoperability.

Expected: A capabilities object with boolean flags matching actual implementation.

On failure: If unsure whether a capability will be implemented, set it to false. Capabilities can be added in future versions. Removing a capability is a breaking change.

Step 5: Validate and Publish Agent Card

5.1. Assemble the complete Agent Card:

{
  "name": "data-analysis-agent",
  "description": "Performs statistical analysis and visualization on tabular datasets.",
  "url": "https://agent.example.com",
  "version": "1.0.0",
  "provider": {
    "organization": "Example Corp",
    "url": "https://example.com"
  },
  "authentication": {
    "schemes": ["oauth2"],
    "credentials": { ... }
  },
  "capabilities": {
    "streaming": true,
    "pushNotifications": false,
    "stateTransitionHistory": true
  },
  "skills": [ ... ],
  "defaultInputModes": ["text/plain"],
  "defaultOutputModes": ["text/plain"]
}

5.2. Validate the Agent Card:

• Parse as JSON and verify no syntax errors
• Verify all required fields are present (name, description, url, skills)
• Verify each skill has id, name, description, and at least one input/output mode
• Verify the URL is reachable and serves the card at /.well-known/agent.json

5.3. Publish the Agent Card:

• Serve at https://<agent-url>/.well-known/agent.json
• Set Content-Type: application/json
• Enable CORS headers if cross-origin discovery is needed
• Register with any relevant agent directories or registries

5.4. Test discovery by fetching the card:

curl -s https://agent.example.com/.well-known/agent.json | python3 -m json.tool

Expected: A valid JSON Agent Card served at the well-known URL, parseable by any A2A client.

On failure: If JSON validation fails, use a JSON linter to identify syntax errors. If the URL is not reachable, check DNS, SSL certificates, and web server configuration. If CORS is needed, add Access-Control-Allow-Origin headers.

Validation

• Agent Card is valid JSON with no syntax errors
• All required fields are present: name, description, url, skills
• Each skill has id, name, description, inputModes, and outputModes
• Authentication scheme matches deployment security requirements
• Capability flags accurately reflect implementation status
• Agent Card is served at /.well-known/agent.json with correct Content-Type
• A2A clients can fetch and parse the card successfully
• Examples in skills are realistic and trigger the correct skill

Common Pitfalls

• Overpromising capabilities: Setting streaming: true or pushNotifications: true without implementation causes client failures when those features are used. Be conservative.
• Vague skill descriptions: Descriptions like "does data stuff" prevent accurate skill matching. Be specific about inputs, outputs, and domains.
• Missing CORS headers: Browser-based A2A clients cannot fetch the Agent Card without proper CORS configuration.
• Skill overlap: If two skills could handle the same task, client agents cannot determine which to invoke. Ensure clear boundaries.
• Forgetting default modes: If defaultInputModes and defaultOutputModes are omitted, clients may not know what content types to send.
• Version stagnation: Update the Agent Card version when skills or capabilities change. Clients may cache old versions.
• Publishing before implementation: The Agent Card is a contract. Publishing skills that are not yet implemented leads to runtime failures.

Related Skills

• implement-a2a-server - implement the server behind the Agent Card
• test-a2a-interop - validate Agent Card conformance and interoperability
• build-custom-mcp-server - MCP server as alternative/complement to A2A
• configure-mcp-server - MCP configuration patterns applicable to A2A setup