ATH supports three discovery modes, from simplest to most sophisticated. Implementations MUST support at least one.

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Mode 1: Manual Configuration

The agent is directly configured with service endpoints. No discovery protocol needed. 
{
  "provider": "example-service",
  "api_base": "https://api.example.com/v1",
  "oauth": {
    "authorization_url": "https://example.com/oauth/authorize",
    "token_url": "https://example.com/oauth/token"
  }
}
Use case: Development, testing, internal tools, or when using an OAuth bridge that already has provider configurations.

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Mode 2: Gateway Catalog Discovery

This is the recommended discovery mode for Gateway Mode deployments.
An ATH-compliant gateway MAY publish a provider catalog at a well-known endpoint: Endpoint: GET https://<gateway>/.well-known/ath.json 
{
  "ath_version": "0.1",
  "gateway_id": "ath-gateway.example.com",
  "agent_registration_endpoint": "https://ath-gateway.example.com/ath/agents/register",
  "supported_providers": [
    {
      "provider_id": "example-mail",
      "display_name": "Example Mail",
      "categories": ["email", "productivity"],
      "available_scopes": ["mail:read", "mail:send", "mail:delete"],
      "auth_mode": "OAUTH2",
      "agent_approval_required": true
    }
  ]
}
Implementations MAY auto-generate this catalog from their configured OAuth bridge.

​
Mode 3: Service-Side Discovery

Services publish ATH metadata at a well-known endpoint for direct agent-to-service discovery. This is the discovery mode for Native Mode deployments. Endpoint: GET https://<service-domain>/.well-known/ath-app.json 
{
  "ath_version": "0.1",
  "app_id": "com.example.mail",
  "name": "Example Mail API",
  "auth": {
    "type": "oauth2",
    "authorization_endpoint": "https://example.com/oauth/authorize",
    "token_endpoint": "https://example.com/oauth/token",
    "registration_endpoint": "https://example.com/developers",
    "scopes_supported": ["mail:read", "mail:send"],
    "agent_attestation_required": true
  },
  "api_base": "https://api.example.com/v1"
}
Use case: Services that natively support ATH.

​
Choosing a Discovery Mode

ModeWhen to useEffort
ManualDevelopment, testing, single known providerNone
Gateway CatalogGateway deployments with multiple providersLow (automatic if using reference implementation)
Service-SideNative ATH implementationsMedium (service publishes .well-known/ath-app.json)