Fern · Schema

Fern API Definition

Schema describing a Fern-managed API definition. A Fern project can be authored from one of several upstream sources (OpenAPI, AsyncAPI, Protobuf, OpenRPC, or the Fern Definition Language) and produces SDKs and documentation as outputs.

Agent ReadyAIAPI DefinitionsAsyncAPICode GenerationDeveloper ExperienceDeveloper PortalDocumentationgRPCllms.txtMCPOpenAPIOpenRPCPlatformProtobufSDKsWebSockets

Properties

Name	Type	Description
id	string	Stable identifier for the API definition inside a Fern project.
name	string	Human-friendly API name.
version	string	API version string, semantic version preferred.
description	string	Free-form description of the API.
source	object	Upstream source of truth that Fern reads to generate SDKs and docs.
protocols	array	Wire protocols this API exposes.
auth	object	Authentication scheme metadata for SDK generators and docs.
environments	array	Named environments (e.g. production, sandbox) used by generated SDKs.

View JSON Schema on GitHub

JSON Schema

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://raw.githubusercontent.com/api-evangelist/fern/main/json-schema/fern-api-definition-schema.json",
  "title": "Fern API Definition",
  "description": "Schema describing a Fern-managed API definition. A Fern project can be authored from one of several upstream sources (OpenAPI, AsyncAPI, Protobuf, OpenRPC, or the Fern Definition Language) and produces SDKs and documentation as outputs.",
  "type": "object",
  "required": ["id", "name", "source"],
  "properties": {
    "id": {
      "type": "string",
      "description": "Stable identifier for the API definition inside a Fern project."
    },
    "name": {
      "type": "string",
      "description": "Human-friendly API name."
    },
    "version": {
      "type": "string",
      "description": "API version string, semantic version preferred."
    },
    "description": {
      "type": "string",
      "description": "Free-form description of the API."
    },
    "source": {
      "type": "object",
      "description": "Upstream source of truth that Fern reads to generate SDKs and docs.",
      "required": ["type"],
      "properties": {
        "type": {
          "type": "string",
          "enum": ["openapi", "asyncapi", "protobuf", "openrpc", "fern-definition"]
        },
        "path": {"type": "string"},
        "url": {"type": "string", "format": "uri"},
        "overrides": {"type": "string"}
      }
    },
    "protocols": {
      "type": "array",
      "description": "Wire protocols this API exposes.",
      "items": {
        "type": "string",
        "enum": ["rest", "websocket", "grpc", "webhook", "json-rpc"]
      }
    },
    "auth": {
      "type": "object",
      "description": "Authentication scheme metadata for SDK generators and docs.",
      "properties": {
        "schemes": {
          "type": "array",
          "items": {
            "type": "string",
            "enum": ["bearer", "basic", "api-key", "oauth2", "jwt", "header", "custom"]
          }
        }
      }
    },
    "environments": {
      "type": "array",
      "description": "Named environments (e.g. production, sandbox) used by generated SDKs.",
      "items": {
        "type": "object",
        "required": ["name", "url"],
        "properties": {
          "name": {"type": "string"},
          "url": {"type": "string", "format": "uri"},
          "default": {"type": "boolean"}
        }
      }
    }
  }
}