Multi-language SDKs

Multi-language SDKs

Callspec’s own TypeScript client is generated from callspec.json (SDK generation). For other languages, export OpenAPI and point any OpenAPI-compatible tool at it.

Export OpenAPI

From a running server (replace the host (127.0.0.1), port (3000), and mount (/v1) with yours):

bash

curl -fsS http://127.0.0.1:3000/v1/openapi.json -o openapi.json

Or emit offline with emitOpenApi — see OpenAPI.

Generators

Feed that openapi.json into the generator you prefer. Two common options:

Tool	Notes
Fern	Multi-language SDKs and hosted API docs
Microsoft Kiota	Open-source clients from OpenAPI (C#, Go, Java, Python, TypeScript, …)

Keep Callspec for your TypeScript app (Result-typed ApiClient, MCP, docs UI). Use Fern, Kiota, or similar when you need SDKs or docs outside that stack.

Related

• OpenAPI — what’s in /openapi.json and how to emit it
• SDK generation — TypeScript from callspec.json