For AI agents: a documentation index is available at the root level at /llms.txt and /llms-full.txt. Append /llms.txt to any URL for a page-level index, or .md for the markdown version of any page.
Book a demoLog inStart for free
  • Overview
    • What is an API definition?
    • Project structure
      • Overview
      • Overrides
      • Authentication
      • Servers
      • Sync your specification
Checking status...
SOC2Soc 2 Type II
© 2026 Fern • Birch Solutions, Inc., a Postman company

Documentation

SDKsDocsAsk FernCLI Reference

API Definitions

OpenAPIAsyncAPIOpenRPCgRPC

Resources

BlogSupportPricing

Company

Brand KitPrivacy PolicyTerms of Service
LogoLogo
Book a demoLog inStart for free
On this page
  • Transport protocols
  • HTTP/HTTPS transport
  • WebSocket transport
  • TCP transport
  • Server variables
  • Multiple environments
  • Server-specific configurations
  • Load balancing and multiple URLs
  • WebSocket-specific configurations
  • Security configurations
  • Transport-specific optimizations
OpenRPC

Servers

Define server URLs and transport mechanisms for your JSON-RPC API

||View as Markdown|
Was this page helpful?
Edit this page
Previous

Authentication

Next

Sync your OpenRPC specification

OpenRPC allows you to specify one or more server configurations that define how clients can connect to your JSON-RPC API.

openrpc.yml
1servers:
2  - name: production
3    url: https://api.yourcompany.com/rpc
4    description: Production HTTP JSON-RPC server
5  - name: websocket
6    url: wss://api.yourcompany.com/rpc
7    description: Production WebSocket JSON-RPC server

Specifying servers is valuable for both SDKs and Docs:

  • For SDKs, your users won’t need to manually specify the server URL at client instantiation
  • For Docs, your API playground will automatically connect to the correct server

Transport protocols

JSON-RPC can be used over various transport protocols:

HTTP/HTTPS transport

openrpc.yml
1servers:
2  - name: http-production
3    url: https://api.yourcompany.com/rpc
4    description: HTTPS JSON-RPC endpoint
5  - name: http-staging
6    url: https://staging-api.yourcompany.com/rpc
7    description: Staging HTTPS endpoint

WebSocket transport

openrpc.yml
1servers:
2  - name: websocket-production
3    url: wss://api.yourcompany.com/rpc
4    description: WebSocket JSON-RPC for real-time communication
5  - name: websocket-dev
6    url: ws://localhost:8080/rpc
7    description: Development WebSocket server

TCP transport

openrpc.yml
1servers:
2  - name: tcp-production
3    url: tcp://api.yourcompany.com:9090
4    description: TCP JSON-RPC server for high-performance applications

Server variables

Use variables to make your server configurations more flexible:

openrpc.yml
1servers:
2  - name: production
3    url: https://{environment}.api.yourcompany.com/rpc
4    description: Production JSON-RPC server
5    variables:
6      environment:
7        default: prod
8        enum:
9          - prod
10          - staging
11          - dev
12        description: Environment name

Multiple environments

Configure different environments with appropriate descriptions:

openrpc.yml
1servers:
2  - name: production
3    url: https://api.yourcompany.com/rpc
4    description: Production environment - high availability, rate limited
5  - name: staging
6    url: https://staging-api.yourcompany.com/rpc
7    description: Staging environment - for testing new features
8  - name: development
9    url: http://localhost:8080/rpc
10    description: Local development server
11  - name: sandbox
12    url: https://sandbox-api.yourcompany.com/rpc
13    description: Sandbox environment - safe for testing

Server-specific configurations

Add server-specific metadata and configurations:

openrpc.yml
1servers:
2  - name: production
3    url: https://api.yourcompany.com/rpc
4    description: Production JSON-RPC server
5    variables:
6      version:
7        default: v1
8        enum: [v1, v2]
9        description: API version
10    summary: High-performance production server
11    tags:
12      - name: production
13        description: Production environment

Load balancing and multiple URLs

Configure multiple server URLs for load balancing:

openrpc.yml
1servers:
2  - name: primary
3    url: https://api-primary.yourcompany.com/rpc
4    description: Primary production server
5  - name: secondary
6    url: https://api-secondary.yourcompany.com/rpc
7    description: Secondary production server (fallback)
8  - name: regional-us
9    url: https://us.api.yourcompany.com/rpc
10    description: US regional server
11  - name: regional-eu
12    url: https://eu.api.yourcompany.com/rpc
13    description: EU regional server

WebSocket-specific configurations

Configure WebSocket servers with connection parameters:

openrpc.yml
1servers:
2  - name: websocket-main
3    url: wss://api.yourcompany.com/rpc
4    description: Main WebSocket JSON-RPC server
5    variables:
6      protocol:
7        default: "jsonrpc-2.0"
8        description: JSON-RPC protocol version
9      heartbeat:
10        default: "30"
11        description: Heartbeat interval in seconds

Security configurations

Configure authentication and security at the server level:

openrpc.yml
1servers:
2  - name: secure-production
3    url: https://api.yourcompany.com/rpc
4    description: Secure production server with authentication
5    security:
6      - bearerAuth: []
7      - apiKeyAuth: []
8components:
9  securitySchemes:
10    bearerAuth:
11      type: http
12      scheme: bearer
13    apiKeyAuth:
14      type: apiKey
15      in: header
16      name: X-API-Key

Transport-specific optimizations

Configure servers for specific use cases:

openrpc.yml
1servers:
2  - name: bulk-operations
3    url: https://bulk.api.yourcompany.com/rpc
4    description: Optimized for batch requests and bulk operations
5  - name: real-time
6    url: wss://realtime.api.yourcompany.com/rpc
7    description: WebSocket server optimized for real-time notifications
8  - name: analytics
9    url: https://analytics.api.yourcompany.com/rpc
10    description: Dedicated server for analytics and reporting methods

Server configurations help clients understand how to connect to your JSON-RPC API and which transport mechanism is most appropriate for their use case.